Method and apparatus for sorting cells

ABSTRACT

A method, apparatus, and system for a sorting flow cytometer include an objective lens having an optical axis coaxially aligned with the flow path at the focal point. A controllable energy source selectively alters an analyte according to a determination of whether the analyte is in a desired sub-population. In various embodiments, one or both of the emission from the controllable energy source and/or the emission from an illumination energy source passes through the objective lens. In some embodiments in which the emission from the controllable energy source passes through the objective lens, the objective lens may focus the emission from the controllable energy source at a different point than the focal point of a signal detected from the analyte and, in particular, at a point closer to the objective lens.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/077,083, filed Jun. 30, 2008, the entire disclosure of which isincorporated herein by reference. This application is related toconcurrently-filed U.S. patent application Ser. No. ______, (attorneydocket no. 30752/44821), the entire disclosure of which is alsoincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates, in general, to methods and apparatus forsorting cells and, in particular, to methods and apparatus for using acontrolled energy source to modify a population of cells of interest byselectively removing, enriching, or altering cells, viruses, orparticles from the population.

BACKGROUND

Flow cytometric sorting permits the selection, enrichment,apportionment, or division of populations of cells, viruses, bodies orparticles of interest (hereinafter referred to as cells). The selectioncriteria include measurable properties of individual cells that can bedetected from outside the cell, with or without the aid of chemicalreagents or of complexes or bodies that are, or that may be caused tobe, associated with the cell. For instance, properties of cells may bemeasured or approximated by detecting and/or quantifying the associationof the cells with one or more labels, such as molecules, complexes, orbodies that fluoresce or have been modified to be rendered fluorescent.Such fluorescent molecules, complexes, and/or bodies may differentiallyassociate with cells on the basis of qualitative or quantitativeproperties of the cells, including their composition with respect toproteins, lipids, phosphoproteins, glycoproteins, phospholipids,glycolipids, nucleic acids (including the quantity, sequence, ororganization of nucleic acids), carbohydrates, salts/ions, and any othermolecules in, on, or associated with the cells. Further, suchfluorescent molecules, complexes, and/or bodies may differentiallyassociate with cells based on physical or physiological characteristicsof the cells, examples of which include but are not limited to membranepermeability, membrane composition, membrane fluidity, chemical ormembrane potential, viability, chemical gradients, motility, reductionor oxidation potential or state, and other parameters or properties.

Other measurable properties of cells, whether labeled or unlabelled,modified or unmodified, that may provide a basis for cell selection mayinclude but are not limited to:

properties of light interacting with the cells, such as fluorescence,absorbance, reflectance, scatter, polarization, or other properties;

electrical properties of the cells or of the effect of the cells ontheir environment, including conductance, inductance, resistance,membrane potential or voltage, or other properties;

magnetic or electromagnetic properties of cells, including magnetism,paramagnetism, magnetic resonance, and/or interaction of the cells withelectromagnetic energy;

the appearance, image, or morphological properties of the cells; and

the makeup of the cells with respect to any substance or parameter,measured directly or indirectly in any way.

Furthermore, the measurement of such parameters, directly or indirectly,singularly or in combination, may reflect simple or complex propertiesof interest of the cells.

One example of such a property is the sex chromosome included in thediploid, haploid, or gamete genome, which may be an X chromosome or a Ychromosome or combinations of both depending on the cell type and theorganism. The determination of sex chromosome content may be inferredusing direct or indirect measurements or determinations using one ormore methods. Such methods include the measurement of the DNA content ofthe cells determined relatively or absolutely; the presence or absenceof certain DNA sequences, or markers of the presence or absence ofcertain DNA sequences; the size of the cells or of portions ororganelles of the cells; the presence, localization, or absence ofproteins or other markers characteristic of the sex chromosome contentof the cells, or combinations or patterns of expression of such markers;or any other measurement that reflects the sex chromosome composition ofthe cell. Many other such measurements may be made, or propertiesdetermined, to identify cells that are of interest in a particularinstance, situation, system, disease, condition, process, orcircumstance.

Such cytometric measurements permit quantitative and/or qualitativedeterminations about cells, populations of cells, organs, tissues, ororganisms. Such determinations may be used in many ways including butnot limited to diagnosis, biomedical research, engineering,epidemiology, medicine, agriculture, animal husbandry, livestockmanagement, zoology, biopharmaceutical industry, and other fields. Inaddition to the ability to perform such measurements, current methodsand instrumentation permit the separation of cells based oncharacteristics or parameters measured by cytometry as described above.Cells can be selected positively or negatively by the concentration,collection, or partitioning of cells of interest or by the removal ofcells that are not desired or of interest in the preparation. Suchselection can be controlled on the basis of any parameter,characteristic, or combination of parameters or characteristics that canbe determined as described above.

Cells identified by methods including or related to those describedabove can be separated, partitioned, concentrated, depleted, orcollected into any arbitrary number of groups. One common separationmethod (depicted in FIG. 1A) uses electrostatic forces to divert anelectrically or electrostatically charged stream, droplet, or dropletscontaining a cell or cells having desired or undesired properties. Thediverted cells are collected or discarded as appropriate to theparticular application, as illustrated in FIG. 1A. Other separationmethods include the use of fluidic devices including valves to divertcells in a fluid stream to alternate pathways, channels, tubes, orelements for subsequent collection or disposal, as illustrated in FIG.1B.

There exist a number of methods and systems for performing flowcytometric sorting of cells. Among these are methods and systemsdesigned specifically to perform flow cytometric sorting of mammaliansperm cells and, in particular, to sort the sperm cells into populationsof sperm cells bearing X chromosomes and/or populations of sperm cellsbearing Y chromosomes, with the purpose of increasing the probabilitythat fertilization of an egg with the sorted sperm will result inoffspring with a desired gender. For example, a dairy farmer may desireto sort the sperm of a bull so that bovine embryos may be produced, byartificial insemination, in vitro fertilization, or other means, withsperm having an X chromosome to produce additional female bovineoffspring.

Flow cytometric sorting methods present a number of challenges,particularly with respect to sorting mammalian sperm cells for later usein producing offspring. Importantly, methods used to label and/or todifferentiate between the cells and/or methods used to sort the cellsmust not adversely affect the viability of the cells. Often, one or moregoals of the methods and/or systems involved (e.g., faster sorting,improved accuracy, etc.) conflict with other goals of the methods and/orsystems. Various factors must be balanced and considered, including thetemperatures, temperature changes, pressures and/or pressure changes towhich the cells are subjected, the fluidic environments to which thecells are exposed, the forces applied to the cells, and the lifespan ofthe cell. For example, the rate at which a fluorescent molecule (e.g., afluorochrome) enters a cell to bind to DNA within the nucleus of thecell (i.e., the rate at which cells may be stained), may increase astemperature increases. Thus, the throughput of a system (at least thethroughput of the staining process) may increase with an increase in thetemperature of the cells' environment. However, increased temperaturemay prove detrimental to the viability of the cells and/or the length oftime that the cells remain viable. By contrast, maintaining the cells atthe optimal temperature for viability may increase the time required forstaining (and measuring and sorting) the cells, such that the processtakes longer than is practical or such that the cells are not viableafter the time required to complete the process.

Another challenge associated with sorting cells relates to the physicaland optical properties of the cells. In particular, flattened orotherwise asymmetrical cells, such as mammalian red blood cells or spermcells, exhibit anisotropic emission of energy (e.g., light). The complexgeometries of a cell's interior and/or the complex geometries of thecell's boundaries act to refract and/or reflect light in ways that arehighly dependent on the orientation of the cell with respect to anyillumination sources and/or detectors used to differentiate betweencells. For example, flow cytometry sorting of mammalian sperm cells intopopulations having X or Y chromosomes usually involves staining thecells with a fluorescent molecule that binds to DNA within the cells.The variation in DNA content between the X and Y chromosomes of mostmammalian species (Y chromosomes generally containing less DNA than Xchromosomes) results in relatively greater fluorescence from cellscontaining X chromosomes. However, the difference in DNA content of Xand Y chromosomes is typically on the order of only a few percent and,often, cell geometry and/or orientation can affect the detectedfluorescence by a percentage that far exceeds the percentage differencein DNA content between the X and Y chromosomes. Additionally, suchanalysis requires that cells pass through the detection region singly,such that a detector does not interpret fluorescence from two cells asfluorescence from a single cell.

Flow cytometry sorting systems frequently employ a core-in-sheathfluidic mechanism to carry the cells through the detection region. Asdepicted in FIG. 1C, a relatively slow moving stream 50 of an aqueoussuspension of cells 52 is injected into a relatively faster moving flow54 of sheath fluid. This arrangement focuses the cells 52 into a stream56, referred to as the core stream. With appropriate selection of thepressures and consequent velocities of the core suspension and sheathfluid, the core stream is narrowed by hydrodynamic forces exerted by thesheath flow, and the cells in the core stream are distributedlongitudinally such that they are carried one by one in the flow. Theforces that elongate and narrow the core stream have the additionalbenefit of orienting the cells 52 such that a lengthwise axis 58 of thecell 52 is parallel to the direction of flow of the single file stream56. However, the orientation of the cells about the lengthwise axis 58remains more or less random. Thus, as each cell 52 passes through thedetection area, light incident upon the cell, light emitted from thecell (e.g., fluorescent light), and light reflected off of the cell,remains dependent on the orientation of the cell 52. This is especiallytrue of many types of mammalian sperm cells.

There are a number of solutions to the problem of sperm cell orientationwith respect to illumination and detection of cells within flowcytometry systems. For example, FIG. 1D illustrates one solution, whichsolution employs a cut, beveled tip 60 on a tube 62 injecting a samplestream 64 into a sheath flow 66. The flattened, beveled tip 60 helps toorient the cells about their lengthwise axes 58 within the sheath flow66 such that the flat faces of the cells tend to align in a consistentdirection. Another solution (which may be combined with the beveled tipsolution) employs two detectors 68 and 70 orthogonal to each other (a0-degree detector 68 and a 90-degree detector 70) which are used incombination to estimate the orientation of each cell 52 as it passesthrough a detection area 72 and to measure the fluorescence of thosecells that are found to be appropriately oriented such that precisequantization of the fluorescent signal is possible. The solutionsemploying hydrodynamic orientation of cells around the lengthwise axisgenerally yield populations in which the desired alignment forfluorescence measurement is achieved for about 70% or less of the cellsin the sample flow, which decreases the throughput of the instrument andresults in the discarding of improperly oriented cells.

Still another solution to the problems associated with cell geometry andorientation utilizes optical detection along the same axis as thecore-in-sheath flow that carries the cells. In one such solution,epi-illumination optics are used to illuminate the cell and detect lightemitted by the cell. As depicted in FIG. 1E, a sample stream 74 carriedby a sheath flow 76 travels directly towards a microscope objective lens78, eliminating the dependence on the orientation of the cell (e.g., asperm cell 80) about a lengthwise axis 82 of the cell 80. However, thetrajectory of the cell 80 towards the objective lens 78 requires thatthe cell 80 change trajectory immediately after passing through adetection area 82 (i.e., the focal point 84 of the objective lens 78).The system accomplishes this trajectory change by using a transverseflow 86 of fluid. Uncertainty in the position of individual cells may beintroduced after the analysis by the convergence 88 of the transversefluid flow 86 and the sheath flow 76 and fluid stream 74. Such positionuncertainty may render the system inoperable to perform cell sortingbecause the location of the cell 80 within the converged flow may becomeunpredictable immediately after the cell passes through the detectionarea 82.

Yet another solution, illustrated in FIG. 1F, utilizes one or moreparabolic reflectors 102 to illuminate cells uniformly and/or to collectlight radially from the cells. The system utilizes a nozzle 104 to emita stream/jet 106 of liquid containing individual cells 92. The stream106 moves through a detection region 94 and through a hole 96 in theparabolic reflector 102. At some point after passing through thedetection region, the stream 106 is broken into droplets 90 which may beelectrically charged. Thereafter, each of the droplets 90 may be sortedby, for example, deflecting the charged droplet 90 and electricallycharged deflector plates 98 to deflect the droplets into one or morereceptacles 100. Problematically, this “jet-in-air” configurationsubjects the stream 106 (and the cells 92 contained within the stream106) to a drop in pressure as the stream 106 exits the nozzle 104.Sudden changes in pressure (and the increased pressures within thenozzle itself), can adversely affect the viability of the cell 92 as canthe subsequent impact of the cell 92 into the receptacle 100. Thus, thepressure and speed of the stream 106 exiting the nozzle 104 must remainbelow any threshold that could damage the cells 92, which decreases thethroughput of the system. Additionally, the movement of the droplets 90through the atmosphere may require environmental constraints includingcleanliness of the room air (e.g., a “clean room”) andtemperature-control.

Thus, even with the relatively advanced state of flow cytometry, thereexists an ongoing need in the art to provide more efficient, moresensitive, and more precise methods of and devices for cell separationand/or identification.

SUMMARY

A method and apparatus is described for detecting, selectively alteringby functional and/or physical modification, and collecting desired orundesired cells in a population using flow cytometry. The method doesnot rely on parabolic reflectors or orthogonal detection to detect andcategorize cells, as is the case for common existing cytometric sortingmethods and apparatus. Instead, the method employs an objective lenshaving an optical axis coaxial with the flow of the sample through adetection area. The method may or may not rely on the diversion orbreakup of the flow stream of cells or the assortment of cells todifferent receiving vessels or pathways, as is also the case for commonexisting cytometric sorting methods and apparatus.

The method contemplates the use of a controllable energy source, suchas, but not limited to, an electromagnetic radiation source such as alaser, to irradiate desired or undesired cells in a population that havebeen identified using cytometric detection techniques. The controllableenergy source is selectively directed to cells of interest based ontheir measured properties or characteristics, after their analysis inthe cytometer, in certain aspect within one second of their analysiswhile the cells remain in the fluidic flow of the device. Such cells maybe functionally or physically altered by the imparted energy. Dependingon the particular use and the particular embodiment of the methods orapparatus, the resulting cell population may be functionally orphysically depleted of undesired cells, or may be modified in such a wayas to permit the subsequent enrichment of desired cells or the removalof undesired cells. The described methods and apparatus are broadlyuseful in applications where the enrichment or depletion of cells isrequired. In some embodiments, the method and/or apparatus alters liquidcontaining desired or undesired cells in a population that have beenidentified using cytometric detection techniques, and may not alter thecells directly. In such embodiments, the method and/or apparatus mayrely on the diversion or breakup of the flow stream of cells or theassortment of cells to different receiving vessels or pathways.

One aspect of the described methods and apparatus includes the usethereof for enrichment, selection, functional alteration, or depletionof sperm cells in a population on the basis of the sex chromosome, X orY, contained in the cells. The methods and apparatus include the use ofalternate designs for the fluidics and optical systems of a cytometer,including in one aspect, an apparatus where optical measurementcomponents and/or a cell-altering energy source are/is orientedorthogonal to the fluidic stream, and in another aspect, an apparatuswhere some such components may also or alternatively be oriented in thesame axis as the fluidic stream and/or at oblique angles to it.

The flow cytometric methods and apparatus provide a novel method andapparatus permitting positive or negative selection of cells byobserving the cells and accurately classifying each cell independentlyof the cell's orientation about its longest axis, and subsequently usingthe classification to determine whether to modify, derivatize, damage,kill, or fragment the cell in the course of the cytometry procedure. Thepresently described methods and apparatus incorporate the application offorces, energy, or irradiation to desired or undesired cells coincidentwith or following within one second of the cytometric measurement toeffect changes in those cells that alter them physically orfunctionally. Such altered cells, or their debris or derivatives, are inone aspect retained in the resulting preparation or in other aspects areenriched or removed, depending on the requirements of the particular useor application.

An embodiment is described that permits the functional and/or physicalseparation of spermatozoa bearing X chromosomes from spermatozoa bearingY chromosomes and/or of spermatozoa bearing Y chromosomes fromspermatozoa bearing X chromosomes. In this embodiment, the relative DNAcontent of individual spermatozoa in a population of spermatozoa ismeasured indirectly, utilizing a well known property of DNA-associatingchemicals such as, but not limited to, bisbenzimide, SYBR dyes, such asSYBR-14, Hoechst 33342, Hoechst 33258, ethidium bromide, acridineorange, DAPI, chromomycin, mithramycin, olivomycin and other chemicalsknown in the art that exhibit enhanced fluorescence when associated withDNA. The measurement is accomplished by observing a cell as the cellmoves within a stream flowing toward the observation point, preferablyby an objective lens having an optical axis coaxial with the flow of thestream. Cells containing relatively more DNA (i.e., a higher DNAcontent) are presumed to contain the larger X chromosome, and cellscontaining relatively less DNA (i.e., a lower DNA content) are presumedto contain the smaller Y chromosome. In some embodiments of the methodwhere cells having only one of the sex chromosomes are desired in thefinal preparation, the method utilizes a laser energy source directed tocells, in one aspect, coincident with or in another aspect, within onesecond or less of their analysis, where the laser energy source can berapidly modulated to irradiate cells that contain the undesired sexchromosome and/or cells whose sex chromosome content is uncertain. Inone aspect of this embodiment, the method utilizes a laser energy sourcethat deposits energy of sufficient quality and/or quantity to modify,derivatize, disrupt, disable, and/or kill the undesired cells. Suchchanges in the selected cells involve, in one aspect, the fragmenting ofthe cells or, in an alternative aspect, are less disrupting, dependingon the application. For example, in embodiments of the method whereidentified and/or isolated sperm are to be used for fertilization and/orreproduction, rendering undesired cells incapable of producing viableoffspring, for instance by disruption of the sequence or structure ofDNA molecules in the cells, or by decreasing their motility such thatthey are mostly infertile in use in artificial insemination, is in oneaspect sufficient to produce the desired preparation. In other aspects,the undesired cells are rendered non-motile, killed, modified, orinactivated in some other way to affect the reproductive capacity of theundesired cells. In an alternative aspect, undesired cells are modifiedor derivatized in a way that permits their subsequent removal or partialremoval from the preparation of desired cells.

In another embodiment, the configuration of the cytometer employs one ormore optical elements used, in one aspect, for the measurement ofcellular properties and/or in another aspect, used in the delivery ofenergy to cells, wherein at least one optical element, preferably anoptical axis of an objective lens, is oriented in the same axis as theflow of the cells undergoing analysis. Thus, in some embodiments, amethod and apparatus is provided utilizing an optical element and, inparticular, an objective lens positioned coaxial with the fluid flow,for the illumination, measurement, or delivery of energy to cells. Inanother embodiment, a method and apparatus is provided utilizing one ormore additional optical elements, alone or in combination, positioned at90 degrees to the fluid stream for measurements or for the delivery ofenergy to cells. In still another embodiment, a method and apparatus isprovided utilizing one or more additional optical elements, alone or incombination, positioned non-coaxial to the fluid stream for measurementsor for the delivery of energy to cells. In yet another embodiment, amethod and apparatus is provided utilizing one or more additionaloptical elements, alone or in combination, positioned at an obliqueangle to the fluid stream for measurements or for the delivery of energyto cells. As used herein, an “oblique angle” is an angle, such as anacute or obtuse angle, that is not a right angle or a multiple of aright angle.

Some embodiments provide a method for modifying a cell of interest in apopulation of cells comprising the step of contacting the cell ofinterest with a controllable energy source that modifies the cell ofinterest upon identification of a cell as a cell of interest in apopulation of cells, without separating the cell of interest from thepopulation of cells upon modification by the energy source.

Some embodiments provide a method for identifying a subpopulation ofcells of interest in a population of cells, comprising the step ofcontacting the population of cells with a controllable energy sourcethat modifies cells of the subpopulation of cells of interest, whereincontacting takes place after a first analysis of the cells in a fluidicsample flow of a flow cytometer, and no longer than about one secondafter the first analysis, the cells remaining within the fluidic sampleflow of the flow cytometer, wherein the first analysis identifies cellsof the subpopulation of cells as cells of interest, as those cells ofinterest flow toward an interrogation area, and wherein the controllableenergy source modifies the cells of interest in the sample flow throughthe flow cytometer.

In some embodiments, the first analysis comprises detecting the cells ofinterest as having a desired property selected from the group consistingof a desired: protein composition, DNA composition, cell surface marker,molecule size, light absorbance, light reflection, fluorescence, lightscatter, polarization, electrical property, magnetic property,morphological property, membrane permeability, membrane fluidity andredox state.

In some embodiments, contacting the population of cells with the energysource occurs as the population of cells passes through a flow stream ina flow cytometer. In a related embodiment, the cell of interest iscontacted with the energy source after, and within one second of, theidentification of the cell as a cell of interest in the flow stream.

It is contemplated, in some embodiments, that the energy source ispositioned co-axial to the flow stream. It is further contemplated thatthe energy source is positioned at a 90° angle to the flow stream, orpositioned at an angle oblique to the flow stream. In anotherembodiment, the energy source is delivered to cells of interest viaKöhler and/or epi-illumination optics. In another embodiment, the energysource is directed to a point in the flow of cells that is downstream ofthe position at which the cellular properties are measured. In anotherembodiment, the energy source is directed to a point in the flow ofcells that is downstream of the position at which the cellularproperties are measured and is after a diversion or turning of the flowstream from its original direction of flow.

In some embodiments, one or more analyses are accomplished by observinga cell as the cell moves within a stream flowing toward an observationpoint, preferably by an objective lens having an optical axis coaxialwith the flow of the stream. After passing through the observationpoint, the stream changes directions in some embodiments, while theorder and/or location of the cells within the stream remaindeterminable. In some embodiments, a controllable energy source mayselectively alter one or more of the cells according to the one or moreanalyses. In some embodiments, the controllable energy source ispositioned coaxial to the newly directed stream, while in otherembodiments, the controllable energy source is positionedperpendicularly or at an oblique angle relative to the newly directedstream. In some embodiments, which may or may not include a controllableenergy source, a nozzle may eject stream, forming droplets that may besorted using known means (e.g., by using a controllable energy source toapply an electrostatic charge, controlling pressure in various fluidflow pathways, etc.).

In some related embodiments, the controllable energy source is directedto the location of the cell in a flow stream in a manner selected fromthe group consisting of continuous stream, pulsed stream, intermittenton/off cycles, periodic focus and defocus of the energy source andintermittent rapid diversion of the energy source to the stream.

In some embodiments, the controlled energy source is an electromagneticsource. In some embodiments, the energy source is a laser.

In some embodiments, the modification of the cells is selected from thegroup consisting of derivatizing, killing, damaging, disrupting andfragmenting the cells of interest.

In a further aspect, the cell of interest is identified as a cell ofinterest using a label detectable by electrical, magnetic,spectroscopic, photochemical, biochemical, immunochemical, fluorescent,or other chemical means. In some embodiments, the label is the additionof a photoactivatable chemical compound or label.

In a related embodiment, the cell of interest is identified as having adesired property selected from the group consisting of a desired:protein composition, protein content, DNA composition, DNA content, cellsurface marker, molecule size, light absorbance, light reflection,fluorescence, light scatter, polarization, electrical property, magneticproperty, morphological property, membrane permeability, membranefluidity and redox state.

The described methods and apparatus contemplate that any energy source,detector, or focusing element used in the detection of properties ofcells in the flow may be positioned co-axial to the flow stream. Forexample, in a flow cytometer comprising detectors and a controllableenergy source, either the detectors or the controllable energy source,or both, are positioned co-axial to the flow stream. In a relatedembodiment, any detection apparatus and or optical elements used in thedetection of properties of cells in the flow is positioned coaxial tothe flow stream.

In a further embodiment, Köhler and/or epi-illumination optics are usedfor the delivery of light or energy used for the detection of desiredproperties. In a related embodiment, when the method uses a flowcytometer, the flow cytometer is an epi-illumination cytometer. It isfurther contemplated that an epi-illumination cytometer useful in thedescribed method incorporates apparatus for the modification of cells ofinterest as further described herein.

When a flow cytometer is used in the described method, the flowcytometer is a flow cytometer having one or more sample streams andincorporates optics having an objective lens coaxial with the flow ofthe one or more sample streams for the delivery of light or energy usedfor the detection of desired properties, for the detection of desiredproperties of cells, and/or for the delivery of light or energy used forthe modification of desired or undesired cells.

In a further embodiment, the energy source modifies the cell of interesthaving a desired property. In a related embodiment, the energy sourcemodifies the cell of interest lacking a desired property.

In a still further embodiment, the cell of interest is a sperm cellselected from the group of X chromosome-bearing sperm and Ychromosome-bearing sperm. It is contemplated, in some embodiments, thatthe sperm cell is identified as a cell of interest based on a desiredproperty of difference in DNA content between X chromosome-bearing spermand Y chromosome-bearing sperm.

The described methods and apparatus further provide that the populationof cells are collected in a collection chamber for further use. In someembodiments, the collection chamber contains cells of interest whichhave been modified by the controllable energy source and cells that havenot been modified by the controllable energy source. In a relatedembodiment, after collection, the cells of interest may be used insubsequent processes or procedures. In a still further embodiment, it iscontemplated that after collection, the cells of interest are discardedand the reminder of the population of cells are used in subsequentprocesses or procedures.

The described methods and apparatus also provide an apparatus formodifying a cell of interest in a population of cells comprising acontrollable energy source that modifies the cell of interest uponidentification of a cell as a cell of interest in a population of cells,without separating the cell of interest from the population of cellsupon modification by the energy source.

In a related embodiment, the described methods and apparatus contemplateidentifying a subpopulation of cells of interest from a population ofcells, using a flow cytometer comprising a controllable energy sourcethat modifies the subpopulation of cells of interest wherein thecontacting takes place after a first analysis of the cells during sampleflow through a sample tube of the flow cytometer, and usually within onesecond of the cell analysis, while the cells remain within the fluidicsample flow of the apparatus, wherein the first analysis identifies thecell as a cell of interest, and wherein the controllable energy sourcemodifies the cell of interest during the sample flow through the flowcytometer.

In some embodiments, one or more steps of a described method are storedas machine-readable instructions on a tangible storage medium within acontroller. A processor of the controller executes the instructions tomonitor and/or control various aspects of a sorting flow cytometer. Theinstructions may be embody one or more routines adapted to various taskswithin the cytometer.

In some additional embodiments, an optical cell, cuvette, window, flowtube, wall, boundary, or other part of a sorting flow cytometer isformed of a material having an index of refraction between 1.30 and1.40, inclusive. In these and other embodiments, an analyte-bearingsolution may be adjusted such that the refractive index of the solutionis close to the refractive index of the optical cell, cuvette, window,flow tube, or other part of the sorting flow cytometer and, inparticular, the refractive indices differ by 0.02 or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a droplet sorting method employed in sorting flowcytometers;

FIG. 1B illustrates a differential flow pressure method employed insorting flow cytometers;

FIG. 1C depicts a sheath-and-stream mechanism employed in flow cytometrysystems;

FIG. 1D depicts a sheath-and-stream mechanism that employs a beveled tipto orientate within the stream;

FIG. 1E depicts a flow cytometer detecting a cell using an objectivelens oriented coaxially with the a flow stream;

FIG. 1F illustrates a system using a parabolic reflector to illuminatecells uniformly and to collect light radially from the cells;

FIG. 2 depicts a contemplated embodiment of the flow path of a sortingflow cytometer;

FIG. 3 depicts a contemplated embodiment of a sorting flow cytometer;

FIG. 4 depicts a contemplated alternate embodiment of a sorting flowcytometer;

FIG. 5 depicts another contemplated alternate embodiment of a sortingflow cytometer;

FIG. 6A depicts a contemplated alternate embodiment of a portion of asorting flow cytometer;

FIG. 6B depicts another contemplated alternate embodiment of a portionof a sorting flow cytometer;

FIG. 7 illustrates a method that may be used with one or moreembodiments of a contemplated sorting flow cytometer to create twodifferent focal points for energy within the system;

FIG. 8A depicts an objective lens and associated focal point within aflow path of a contemplated embodiment of the presently describedmethods and apparatus;

FIG. 8B illustrates an embodiment of a generally conical volume formedbetween a nominal focal point and an objective lens;

FIG. 9 depicts a water immersion objective lens and associated focalpoint within a flow path of an embodiment of the presently describedmethods and apparatus;

FIG. 10 depicts a body in which a portion of the flow path of a sortingflow cytometer may be formed, in accordance with an embodiment of thepresently described methods and apparatus;

FIG. 11 depicts an alternate embodiment of the body depicted in FIG. 9;

FIG. 12 depicts another alternate embodiment of the body depicted inFIG. 9;

FIG. 13 depicts still another alternate embodiment of the body depictedin FIG. 9;

FIG. 14 depicts yet another alternate embodiment of the body depicted inFIG. 9; and

FIG. 15 depicts a flow chart illustrating the steps of a method inaccordance with the presently described methods and apparatus.

DETAILED DESCRIPTION

The present specification describes methods, systems, and apparatus forcell separation based on flow cytometry. Unless otherwise defined, alltechnical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skill in the art to which thisthe claimed inventions belong.

It is noted here that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referenceunless the context clearly dictates otherwise.

As persons of ordinary skill in the art will readily appreciate, unlessotherwise indicated as being important to the understanding of thedescribed methods and apparatus, the included figures are not drawn toscale.

As used herein, the following terms have the meanings ascribed to themunless specified otherwise.

The term “cells” refers to the analyte in the described methods andapparatus, this matter including, but not limited to cells, viruses,bodies, or particles. The term “cells of interest” or “cell of interest”refers to a cell having a desired property which property can bedetected during flow of the cell through the flow cytometric apparatus.A “desired property” refers to a certain characteristic thatdistinguishes the cell having the desired property from a cell nothaving said characteristics. Cells having a desired property are withina “desired sub-population” of cells. Exemplary measurable or detectablecell characteristics in a cell of interest include, but are not limitedto, protein composition, protein content DNA composition, DNA content,cell surface markers, molecule size, light absorbance, light reflection,fluorescence, light scatter, polarization, electrical properties of thecells, magnetic properties, morphological properties, membranepermeability, membrane fluidity, and redox state. One of ordinary skillin the art will readily appreciate that a cytometer may measure ordetect any of a number of alternative characteristics in a cell ofinterest, and that these alternative characteristics are readilyamenable to exploitation in the described methods and apparatus. In oneaspect, the methods or apparatus exploit a “desired property” of a cellof interest to identify cells having this property.

The term “first analysis” refers to an initial analysis of cells as thecells proceed through a flow cytometric apparatus, which can be a tube,a cuvette, a region, a cell, a chamber, etc., to determine if the cellsare cells of interest. In an aspect of some embodiments, detectors in aflow cytometer execute the first analysis.

The term “second analysis” as used herein refers to characterization ofthe cell of interest after the first analysis through the flow tube todetermine whether to alter the cell of interest using an energy source.In an aspect of some embodiments, the second analysis takes place after,usually less than one second after, the first analysis.

The terms “modify,” “modification,” “alter,” and “alteration,” as usedherein, refer to using the energy source to induce changes to a cell.Modifications include, but are not limited to, direct effects on thecells, including but not limited to the modification of cellularcomponents or chemicals including proteins, DNA, and substances involvedin cellular metabolism; disruption, heating, cavitation, or explosionsoccurring in or near the cells; permeabilization or perforation ofcells; and destruction, fragmentation, or morphological alteration ofcells. In other aspects, modifications also or alternatively includeindirect effects of the energy source, mediated by the energy source orby other factors, including chemical activation and/or deactivation,chemical crosslinking, or chemical derivitization of the cells or of oneor more cellular components, the activation and/or deactivation of oneor more chemical agents in or near the cells that cause the binding orassociation of such agents or their derivatives to the cell or itscomponents, or the induction of altered functioning of the cells. Incertain aspects, chemical agents, normally present within or otherwiseapplied to the cells, interact with the cells upon irradiation of thecells.

The described methods and apparatus permit identification of cells ofinterest by detecting the presence or absence of any number ofcharacteristics (e.g., a desired property) or parameters that can bedetermined, estimated, or reflected in measurements compatible with flowcytometric techniques. Cytometric measurements used to define cells orcellular populations of interest include in various aspects thosediscussed herein and those otherwise known in the art, as well as novelmeasurement methods, mechanisms, and/or apparatus that may be introducedor made applicable to flow cytometric analysis. Cells subjected tocytometric analysis through practice of the presently described methodsand apparatus, may be labeled or unlabelled, or otherwise modified orunmodified using techniques and reagents known in the art.

As used herein, the term “label” refers to a composition detectable byspectroscopic, photochemical, biochemical, immunochemical, or chemicalmeans. For example, useful labels include fluorescent dyes,electron-dense reagents, enzymes, biotin-streptavidin, dioxigenin,haptens, proteins for which antisera or monoclonal antibodies areavailable, or nucleic acid specific dyes. Thus, in the presentlydescribed methods and apparatus, the makeup, properties, and/orcharacteristic of cells with respect to any substance or parameter,measured directly or indirectly in any way is the basis for theidentification of cells and cell populations for selection or exclusion.

Examples of detectable makeup, properties, and/or characteristics ofcells include, but are not limited to: measurements of properties oflight interacting with the cells or emitted by the cells, such asabsorbance, light scattering, luminescence, fluorescence,phosphorescence, polarization or depolarization of light, or otherproperties; properties of electricity including but not limited toinductance, capacitance, potential, current, or resistance of cells orof the surrounding medium; properties of electromagnetism includingmagnetism, paramagnetism, magnetic resonance, and/or interaction of thecell with or emission of electromagnetic forces and/or waves; imaging,image properties, morphological properties, or related propertiesderived from the collection and/or analysis of image or image-likeproperties of cells. In certain aspects, the measurement is an intrinsicquantity or quality of the cell, or in alternative aspects, themeasurement is a value that indirectly reflects, represents, orapproximates, a quantity or quality of the cell. In still other aspects,the measurement is both an intrinsic quantity or quality of the cell andan indirect reflection, representation, or approximation of a quantityor quality of the cell. By way of example and not limitation, a measureof fluorescence of a cell may reflect the intrinsic fluorescence of thecell or the measure of fluorescence of a cell may reflect the presenceand/or quantity of a fluorochrome or fluorescent particle that binds toor associates with the cell and directly or indirectly reflects someproperty of the cell, or both.

In some aspects of the described methods and apparatus, a sortingcytometer employs a technique that results in the physical or spatialseparation of cells and cell populations. In other aspects of thedescribed methods and apparatus, a sorting cytometer utilizes atechnique that physically and/or functionally modifies selected cells inpopulations to permit their functional and/or physical separation and/ordifferentiation, optionally for subsequent use. In some aspects of thedescribed method and apparatus, a sorting cytometer does not rely onimmediate separation of cells by position, location, vessel, or time,but instead provides cells are that inactivated, incapacitated,disrupted, disarticulated, fragmented, or otherwise altered (i.e.,“modified”) with respect to some desired property, that optionallyallows separation or differentiation of subpopulations in thepreparation. The nature of the modification depends, all or in part, onan intended application or use for identified cells, and thus,characteristics of the identified cells that are relevant in theapplication. For example and for purposes of explanation orclarification only, a malignant or otherwise immortal or rapidly growingcell might be considered functionally inactivated in the context of thepreparation of normal somatic cells if the cell's capacity to reproduceis negatively affected or if the cell is killed. In another example,again for purposes of explanation or clarification only, where anapplication requires the removal from a population of a subpopulation ofcells that produce an undesirable protein or other substance, a sortingcytometer may achieve this result by abrogating production of thesubstance in these cells, by killing the cells, and/or by modifying thecells to permit their physical removal from the population.

The methods and apparatus presently described utilize, in someembodiments, an energy source for modification of cells or for theinduction or initiation of processes such as chemical activation thatmay modify cells. Modifications induced by the energy source include invarious aspects, direct effects on the cells, including but not limitedto the modification of cellular components or chemicals includingproteins, DNA, and substances involved in cellular metabolism;disruption, heating, cavitation, or explosions occurring in or near thecells; permeabilization or perforation of cells; and destruction,fragmentation, or morphological alteration of cells, including cells,viruses, bodies or particles. In other embodiments, modifications alsoor alternatively include indirect effects of the energy source, mediatedby the energy source or by other factors, including chemical activationand/or deactivation, chemical crosslinking, or chemical derivitizationof the cells or of one or more cellular components, the activationand/or deactivation of one or more chemical agents in or near the cellsthat cause the binding or association of such agents or theirderivatives to the cell or its components, or the induction of alteredfunctioning of the cells. In certain embodiments, chemical agents thatreact upon irradiation with the cells are normally present in the cellsor in the application, or they are added as part of the method.

In some embodiments, the described methods and apparatus incorporate theuse of photoactivatable compounds that are induced to bind or associatewith cells or cellular components upon irradiation with light of anappropriate intensity and energy. Such compounds in certain aspectsinduce sufficient crosslinking or denaturation of one or more cellularcomponents that affect cellular processes or metabolism of cells ofinterest. Alternatively, such compounds in certain aspects inducesufficient crosslinking or denaturation of one or more cellularcomponents that kill cells of interest. In another alternative,photoactivatable compounds used in the described methods and apparatusbind to selected cells and alter one or more properties of cells ofinterest in such a way as to render the cells of interest amenable toidentification and/or enrichment and/or depletion in subsequentprocesses. Cells of interest that have been altered by chemicalderivatization, such as the addition of a chemical substance, are incertain aspects removed, concentrated, or purified in a subsequent stepby methods that utilize the properties or interactions of such asubstance. For example, and for purposes of explanation andclarification only, cells of interest are, in one aspect, derivatized bythe addition of a substance that is subsequently bound by an antibodythat permits the capture or retention of the derivatized cell ofinterest by various means. Many such substances are contemplated, and inone aspect, such substances include a class of compounds containing orrelated to the 2,4-dinitrophenyl group (DNP), which in one aspect isrecognized and specifically bound by antibodies recognizing DNP.Accordingly, photoactivatable derivatives of DNP or related compoundsare used in one aspect to derivatize cells of interest in an applicationof this type. Alternatively, derivatized cells of interest are capturedor removed using strategies that cause the derivatized cells of interestto bind preferentially to certain substrates. For example and forpurposes of explanation and clarification only, cells of interestderivatized using compounds containing or related to biotin are in oneaspect captured or retained on substrates, surfaces, substances, media,compounds, or particles that bind or have been modified to bind biotin,for instance by the presence of avidin, streptavidin, biotin-bindingantibodies, or other biotin-binding molecules. In another alternativerelated to this aspect, photoactivatable derivatives of biotin orrelated compounds are used to derivatize cells of interest in such anapplication. Alternately in other aspects, cells of interest are alteredby the addition or association of chemical substances or compoundsbefore being subjected to selection and modification. In such a case,therefore, an embodiment of the methods and apparatus described hereinutilizes alteration of the added substance on selected cells to permitthe differentiation of such cells from others in the population. Forinstance, and for purposes of explanation and clarification only, in oneaspect all cells in a population are derivatized by the addition of aphotolabile chemical compound before analysis, and in one aspect,specific cells are targeted for modification using the energy source ofthe apparatus to modify the photolabile chemical compound on thosecells.

In some embodiments of a cytometer (see FIG. 1), cells pass into aninterrogation or analysis chamber, cuvette, stream, or other analysisposition or region in the usual way, familiar in the art, for flowcytometric analysis and/or sorting. The cytometer identifies cells bytheir measured properties as described above, including but not limitedto such properties as fluorescence and/or light scattering, as having adesired property or not having a desired property in the finalpreparation. A flow of fluid carries the cells through the region of thecytometer and, in one aspect, past one or more laser beams, detectors,and/or other apparatus that detect quantities and qualities of thecells. In one such aspect, the flow of fluid moves the cells toward anoptical element having an axis generally coaxially aligned with thefluid flow. By way of example and not limitation, the optical elementmay include a lens, such as an objective lens, and/or may include one ormore detectors, laser beams, and/or other energy sources. The lightand/or energy passing between the cells and the detectors, laser beams,and or other energy sources may pass through the optical element (e.g.,the objective lens) that is generally coaxially aligned with the flowthe cells through the relevant portion of the cytometer. The position ofeach cell in the cytometer at any point in time is, in one aspect,determined directly or indirectly and/or estimated from the velocity ofthe cell or fluid passing through the relevant portion of theinstrument. A cell that has passed some or all of the analysisposition(s) in the region is, in one aspect, identified as having adesired property or not having a desired property in the finalpreparation. Such a determination is, in one aspect, made by a computerand/or analogue and/or digital electrical or electronic and/or softwareand/or computer hardware data analysis device or devices. Such a devicecompares individual or multiple properties, measurements, and/orcharacteristic of each cell to one or a set or group of properties,measurements, and/or characteristics defined by the operator of theapparatus. Alternatively, the properties to which the measuredproperties are to be compared are, in one aspect, determinedautomatically using algorithms or programs included in or with thecytometer.

The set of properties against which cells measured in the cytometer arecompared in one aspect defines one or more subpopulations of cells ofinterest that have a desired property or do not have a desired propertyin the cell preparation. The determination of whether a cell that ispassing through the analysis region of the instrument is a member of aparticular subpopulation of cells of interest is, in one aspect, maderapidly such that the cell's status as having a desired property or nothaving a desired property in the cell preparation is determined at atime when the position of the cell in the flow system of the instrumentis determined, in certain aspects, usually less than one second afterentering the analysis region of the instrument. Once the determinationhas been made, cells in one aspect are acted upon by an energy or forcethat is selectively imparted to cells that satisfy or do not satisfy theselection criteria. The force or energy in various aspects inactivates,incapacitates, disrupts, disarticulates, fragments, or otherwise altersthe cells of interest with respect to a desired property that isrelevant to an optional subsequent application, or the force or energyin alternative aspects modifies, and/or derivatives, or causes the cellsof interest to be derivatized in a way that permits subsequentseparation or differentiation of one or more subpopulations of cells ofinterest in the preparation.

Such a force or energy, in various aspects, is imparted by one or morelasers or other light and/or electromagnetic sources directed to thelocation of cells in the flowing stream, in such a manner that theenergy source can be rapidly diverted, defocused, or turned off topermit the passage of cells that are not selected for modification. Forexample, and for purposes of clarification and explanation only, a highenergy and/or high intensity laser, capable of being rapidly pulsed orturned on and off, exposes selected cells to damaging radiationrendering them non-functional in the context of any desired use. In someaspects, the force or energy passes through an optical element generallycoaxially aligned with the flow of cells as the cells pass through therelevant area of the cytometer. In any event, all cells, both thoseselected and acted upon by the modifying force or energy, and those notselected and not acted upon by the force or energy, continue to migratewith the cellular flow and exit the region of the apparatus in which themeasurement of cellular properties and the modification of selectedcells is performed. The effluent is collected and it contains modifiedand unmodified cells as well as, in certain aspects, fragments, orresidues of cells, as well as fluid, solutions, and/or buffers used inthe process. In various aspects, the effluent is used further in thisform, or in other aspects it is concentrated, fractionated, or otherwiseprocessed further to achieve desired properties and/or composition.

FIGS. 2-5 depict various embodiments of a sorting flow cytometeraccording to the described methods and apparatus. FIG. 2 in particulardepicts an embodiment of a basic flow path 110 of such a cytometer. Asheath fluid input tube 112 allows pressurized sheath fluid to enter theflow path 110 at a sheath fluid input 114, creating a flow 116 of sheathfluid through the flow path 110. Downstream from the sheath fluid input114 and preferably in a region of smooth, laminar flow of the sheathfluid, an analyte fluid input tube 118 allows a stream 120 of analytefluid (i.e., a fluid in which an analyte is suspended, carried, etc.) toenter the flow path 110 through an analyte input 122. In someembodiments, the analyte input 122 is disposed centrally within the flow116 of sheath fluid and/or centrally within the flow path 110, andoriented such that the stream 120 of analyte fluid is parallel to theflow 116 of sheath fluid as the analyte fluid enters the flow path 110.Of course, the analyte input 122 need not be central to either of theflow 116 of sheath fluid or the flow path 110, and one of ordinary skillin the art could envision embodiments in which the stream 120 of analytefluid is other than parallel to the flow 116 of sheath fluid as thestream 120 of analyte fluid enters the flow path 110. The flow rate andpressure of the flow 116 of sheath fluid relative to the stream 120 ofanalyte fluid compress and constrict the stream 120 of analyte fluid tobe narrow relative to the flow 116 of the sheath fluid. The flow 116 ofsheath fluid and the stream 120 of analyte fluid combine to form asample flow 123.

The flow path 110 may change direction in a region 124, but preferablythereafter includes a region 126 free of both obstacles and abruptchanges in flow direction, and serving to stabilize the sample flow 123before the sample flow 123 reaches an interrogation area 128 (i.e., anobservation area, analysis area, nominal focal point, etc.). The path ofthe sample flow 123 through the flow path 110 defines a flow axis 130.In some embodiments, the stream 120 of analyte fluid and, in particular,the analytes (i.e., the cells) within the stream 120 of analyte fluidgenerally travels through the flow path 110 along the flow axis 130.

After reaching and/or passing through the interrogation area 128, thesample flow 123 is diverted. In some embodiments, the flow path 110changes directions at a corner 132 (indicated in FIG. 2 by a brokenline). In other embodiments, the sample flow 123 encounters a transverseflow 134 as it reaches an end 136 of the region 126. The transverse flow134 redirects the sample flow 123. In some embodiments, the corner 132or the transverse flow 134 causes a 90-degree change in the direction ofthe sample flow 123. However, the sample flow 123 may, in alternativeembodiments, vary by more or less than 90 degrees. In any event, afterchanging direction, the sample flow 123 may flow to a collection vessel138, and may pass through one or more flow path elements 140 (e.g., flowregulators, filters, etc.) before reaching the collection vessel 138.

An objective lens 142 disposed generally at or near the corner 132 or ator near the intersection of the sample flow 123 with the transverse flow134 operates to create a focal point (not shown) within theinterrogation area 128. An optical axis 144 of the objective lens 142 isgenerally coaxially aligned with the flow axis 130 of the flow path 110as the flow path 110 passes through the interrogation area 128. Ofcourse, the optical axis 144 and the flow axis 130 need not be perfectlycoaxial, and may vary such that the optical axis 144 is parallel to andoffset from the flow axis 130, such that the optical axis 144 is at anoblique angle with respect to the flow axis 130, etc.

FIG. 3 illustrates an exemplary sorting flow cytometer 151 includingvarious characteristics of the described methods and apparatus.Similarly to the embodiment of the flow path 110 depicted in FIG. 2,FIG. 3 depicts the sheath flow input tube 112 and the sample fluid inputtube 118, introducing respectively the flow 116 of sheath fluid and thestream 120 of analyte fluid through the sheath fluid input 114 and theanalyte fluid input 122. In particular, the analyte fluid depicted inFIG. 3 includes mammalian sperm cells 150 and a buffer solution 152carrying the mammalian sperm cells 150. As the flow 116 of sheath fluidand the flow 120 of analyte fluid merge to form the sample flow 123, therespective flow rates cause the cells 150 to form a generallysingle-file stream and to align their lengthwise axis (i.e., along thelength of the cells' tail) with the direction of the sample flow 123.

Referring still to FIG. 3, an embodiment of a sorting flow cytometerincludes a first analysis and a second analysis. As the cells 150proceed through the flow path 110 with the sample flow 123, the firstanalysis may determine whether the cells are of interest, may determinethe rate at which the cells are moving through the flow path 110, maydetermine whether, at a given point in the sample flow 123, the cells150 are too close together for one or more later analyses, whether thecells 150 are oriented tail-first or head-first, etc. In the embodimentdepicted by FIG. 3, the first analysis occurs as the cells 150 reach apoint 154 in the flow path 110. A first analysis illumination source 156directs energy 158 toward the point 154. The energy 158 may interactwith each cell 150 to scatter the energy 158 or to otherwise interactwith the cell 150, an antibody associated with the cell 150, afluorochrome (e.g., fluorescein) associated with the cell 150, etc. Adetector 160 may detect resulting energy 162 (e.g., the scatteredenergy, the resulting fluorescent signal, etc.) and send a correspondingsignal via a connection 164 to a controller 166. The detector 160 may bedisposed at any location appropriate to detect the energy 162, includingat an oblique angle from the point 154 (with respect to the illuminationenergy source 156) or in line with the point 154. The first analysisillumination source 156 is preferably a 488 nm laser, but may compriseany energy source suitable for the measurements contemplated in thefirst analysis. The first analysis illumination source 156 may beoriented such that the energy 158 travels perpendicularly to the sampleflow 123 or may, alternatively, be oriented such that the energy 158 isincident upon the cells 150 at an oblique angle to the direction of thesample flow 123. Moreover, the energy 158 and/or the energy 162 may passthrough one or more optical elements (not shown) such as filters,lenses, etc., which may allow either or both of the illumination energysource 156 and the detector 160 to be positioned differently thandepicted by creating a different optical path as generally known in theart.

Some embodiments may omit the first analysis. For example, informationgleaned from the second analysis (described in detail below) may provesufficient both to determine which cells are of interest and todistinguish between cells in desired and un-desired sub-populations.Thus, the elements 154-164 may be omitted in some embodiments.Alternatively, some embodiments may include two or more first analysesand, accordingly, two or more sets of elements 154-164. For example, andwithout limitation, the sample flow 123 may include one or more markers(e.g., included in the sheath flow 116, attached or otherwise associatedwith some cells 150 in the sample stream 120, etc.). A primary firstanalysis may detect one of the markers at a first point, and a secondaryfirst analysis may detect the marker at a second point to determine theflow rate of cells in the sample flow 123.

In any event, the sample flow 123 proceeds after the first analysis tocarry the cells 150 along the flow path 110. As the cells 150 passthrough a point 170, the second analysis characterizes the cells 150, asdescribed below, to determine whether to modify each cell 150. As eachcell 150 reaches the point 170, a second analysis illumination source172 directs energy 174 toward the point 170. The energy 174 may interactwith the cell 150, an antibody associated with the cell 150, afluorochrome (e.g., Hoechst stain) associated with the cell 150 or withDNA within the cell 150, etc. In some embodiments, the second analysisillumination source 172 is an ultraviolet laser emitting the energy 174in the form of ultraviolet radiation that interacts with particles ofHoechst stain attached to the DNA inside of the cell 150 to causefluorescence proportional to the DNA content of the cell 150, asgenerally known in the art. The second analysis illumination source 172may be oriented such that the beam 174 is perpendicular to the sampleflow 123, as depicted in FIG. 3. However, the second analysisillumination source 172 may also be located at an oblique angle withrespect to the sample flow 123. Moreover, the energy 174 may passthrough one or more optical elements (not shown) such as filters,lenses, etc., which may allow the second analysis illumination source172 to be positioned differently than depicted by creating an opticalpath that is not straight.

The interaction of the energy 174 with the cell 150 or with elementsinside the cell 150, causes resulting energy 176 to radiate from thecell 150. The objective lens 142, positioned such that the optical axis144 of the objective lens 142 is generally coaxial with the sample flow123, operates to focus the energy 176. A focal point 178 of theobjective lens 142 is located generally at the point 170, but may belocated so as to detect the resulting energy 176 from the cell 150slightly after the energy 174 illuminates the cell 150 (i.e., the focalpoint 178 may be slightly closer to the objective lens 142 than thepoint 170). A detector 180 situated so as to receive energy 182 focusedby the objective lens 142 detects the focused energy 182 from the cell150, and sends a corresponding signal via a connection 184 to thecontroller 166. Of course, one or more optical elements, such as afilter 186 may act to alter or redirect the energy 182 between theobjective lens 142 and the detector 180. In some embodiments, theobjective lens 142 creates the focal point 178 prior to the corner 132or the convergence of the transverse flow 134 and the sample flow 123.In other embodiments, the objective lens 142 creates a focal point (notshown) at or near the corner 132 or the convergence of the transverseflow 134 and the sample flow 123.

The controller 166, which may include one or more microprocessors 188,one or more crystal oscillators 190, one or more memories 192 storingone or more routines 194, etc., interprets the signals received from thedetector 160 and/or the detector 180, to determine for each cell 150whether the cell 150 is part of a desired sub-population of cells. Forexample, in some embodiments, the cells 150 are mammalian sperm cells,and the controller 166 interprets signals received from the detector 180to determine whether each cell 150 bears an X chromosome or a Ychromosome. As generally known by those of ordinary skill in the art, inmammalian sperm cells Y chromosomes generally contain less DNA than Xchromosomes. Accordingly, by analyzing the fluorescence (i.e., theresulting energy 176) emitted by the stain in the cell 150 uponillumination by the second analysis illumination source 172, thecontroller 166 may generally determine whether the cell 150 carries an Xor a Y chromosome. In some embodiments, one of the routines 194continuously monitors the statistical distribution of detectedfluorescent signals to improve with the passage of time the accuracy ofthe determination.

Still referring to FIG. 3, in some embodiments, the controller 166,according to the determination of whether a cell 150 is part of adesired sub-population, outputs a signal to a controllable energy source196 via a connection 198. The controllable energy source 196 may emitenergy 197 directed at a point 199 in the sample flow 123. In someembodiments, the controller 166 operates to coordinate the signal to thecontrollable energy source 196 and/or the point 199 is selected (e.g.,by aiming, by one or more lenses, mirrors, etc.) according to the rateat which the cell 150 moves through the flow path 110. In someembodiments, the point 199 may be located prior to the corner 132 or theconvergence of the transverse flow 134 and the sample flow 123, tosimplify the determination of the position of the cell 150 travelingalong the flow path 110. In other embodiments, the point 199 may belocated after the corner 132, or may be located at or after theconvergence of the transverse flow 134 and the sample flow 123. In theexample above, the controller 166 may output a signal to cause thecontrollable energy source 196 to emit the energy 197 in response to adetermination that the cell 150 has an X chromosome or in response to adetermination that the cell 150 has a Y chromosome. Alternatively, thecontroller 166 may output a signal to cause the controllable energysource 196 to stop emitting energy 197 in response to a determinationthat the cell 150 has an X chromosome or in response to a determinationthat the cell 150 has a Y chromosome. The energy 197 emitted from thecontrollable energy source 196 may act to disable the cell 150 or renderthe cell 150 non-viable (e.g., by modifying cellular components orchemicals including proteins, DNA, and substances involved in cellularmetabolism; by causing disruption, heating, cavitation, or explosions inor near the cell 150; by causing permeabilization or perforation of thecell 150; and/or by causing destruction, fragmentation, or morphologicalalteration of the cell 150), may act to alter (e.g., by interacting witha chemical in or attached to a cellular component) the cell so that itmay later be identified and/or removed from the desired sub-populationof cells 150, or may act to favorably affect the cell. In someembodiments, the controllable energy source 196 is a laser and, inparticular, may be a laser outputting energy in the visible or infraredparts of the spectrum. In some embodiments, the laser outputs energyhaving a wavelength of 690 nm. In other embodiments, the controllableenergy source 196 may output other types or wavelengths of radiation,such as X-rays, microwaves, visible light, infrared light, ultravioletlight, or any other type of energy having a desired effect on a cell150. Of course, in response to the determination of whether a cell ispart of the desired sub-population the controller 166 may: (1) emitenergy 197 to adversely affect cells 150 determined not to be part ofthe desired sub-population (while leaving alone cells 150 determined tobe part of the desired sub-population); (2) may emit energy 197 topositively affect cells 150 determined to be part of the desiredsub-population (while leaving alone cells 150 determined not to be partof the desired sub-population); (3) may stop emitting energy 197 toavoid positively affecting cells 150 determined not to be part of thedesired sub-population (while continuing to emit energy 197 topositively affect cells 150 determined to be part of the desiredsub-population); or (4) may stop emitting energy 197 to avoid adverselyaffecting cells 150 determined to be part of the desired sub-population(while continuing to emit energy 197 to adversely affect cells 150determined not to be part of the desired sub-population). Moreover, insome embodiments, the controller 166 may treat indeterminate cells 150(e.g., cells 150 for which the controller 166 cannot make adetermination, cells 150 that are too close together, etc.) in the samemanner in which the controller 166 treats cells determined not to be inthe desired sub-population.

FIG. 4 illustrates an exemplary sorting flow cytometer 200 includingvarious characteristics of the described methods and apparatus. Inparticular, the sorting flow cytometer 200 depicted in FIG. 4 omits thefirst analysis and, accordingly, the elements 154-164 do not appear.However, while not illustrated, those of ordinary skill in the art willappreciate that the first analysis may be included, if desired, in theembodiment illustrated in FIG. 4. As in the embodiment depicted in FIG.3, the sample flow 123 carries the cells 150 along the flow path 110. Asthe cells 150 pass through the point 170, the second analysis (which, inthe depiction of FIG. 4 does not follow any first analysis)characterizes the cells 150, as described above, to determine whether tomodify each cell 150. That is, as each cell 150 reaches the point 170,the second analysis illumination source 172 directs the energy 174toward the point 170, and the energy 174 interacts with the cell 150, asdescribed above. Of course, the second analysis illumination source 172may be an ultraviolet laser and the energy 174 may interact withmolecules of Hoechst 33342 stain attached to the DNA inside of the cell150. The second analysis illumination source 172 may be oriented suchthat the beam 174 is perpendicular to the sample flow 123, as depictedin FIG. 4. However, the second analysis illumination source 172 may alsobe at an oblique angle with respect to the sample flow 123. Moreover,the energy 174 may pass through one or more optical elements (not shown)such as filters, lenses, etc., which may allow the second analysisillumination source 172 to be positioned differently than depicted bycreating an optical path that is not straight.

The resulting energy 176 radiating from the cell 150 propagates towardthe objective lens 142, which is positioned such that the optical axis144 (see FIG. 3) of the objective lens 142 is generally coaxial with thesample flow 123, and operates to focus the energy 176. The focal point178 of the objective lens 142 is located generally at the point 170, butmay alternatively be located so as to detect the resulting energy 176from the cell 150 slightly after the energy 174 illuminates the cell150. One or more optical elements may direct the focused energy 182 fromthe objective lens 142 to the detector 180. For example, in theembodiment depicted by FIG. 4, the focused energy 182 passes through abeam splitter 202 and the filter 186 before reaching the detector 180.Other optical elements (e.g., lenses, mirrors, filters, etc.) may alsoaffect the path of the focused energy 182 between the objective lens 142and the detector 180. As in the embodiment depicted in FIG. 3, in someembodiments the objective lens 142 creates the focal point 178 prior tothe corner 132 or the convergence of the transverse flow 134 and thesample flow 123. In other embodiments, the objective lens 142 creates afocal point (not shown) at or near the corner 132 or the convergence ofthe transverse flow 134 and the sample flow 123.

The controller 166, as described above with respect to FIG. 3, operatesto interpret signals received (via the connection 184) from the detector180 (and the detector 160 if the cytometer 200 includes the firstanalysis) to determine for each cell 150 whether the cell 150 is part ofa desired sub-population of cells (e.g., sperm cells with an Xchromosome). The controller 166 outputs a signal over a connection 206to a controllable energy source 204. The controllable energy source 204operates in the same manner as the controllable energy source 196 (FIG.3). However, in the embodiment depicted in FIG. 4, energy 208 emitted bythe controllable energy source 204 passes through the objective lens 142after passing, in some embodiments, through one or more opticalelements, such as a filter 216. The objective lens 142 operates to focusthe energy 208 at a focal point 210. In some embodiments, the objectivelens 142 may focus the energy 208 from the controllable energy source204 such that the focused energy 212 is generally coaxial with thesample flow 123, and such that the point 210 is located closer to theobjective lens 142 than the point 170.

Those of ordinary skill in the art will appreciate that multiple methodsexist for creating both the focal point 210 and the focal point 178using the same lens. FIG. 7 depicts one method that the cytometer 200could employ to create the focal point 178 for the energy 176 and thefocal point 210 for the energy 212. FIG. 7 depicts that as the energy176 (indicated by solid lines in FIG. 7) passes through a lens 214 ofthe objective lens 142 (not shown in FIG. 7) from the focal point 178(i.e., from the cell 150 at the point 170), the lens 214 acts on theenergy 176 such that the rays of energy 176 are parallel as they leavethe lens 214. By contrast, the rays of energy 208 are convergingslightly as they fall incident upon the lens 214 and, accordingly,converge at the focal point 210 after passing through the lens 214. Ofcourse, other methods exist for creating both the focal point 178 andthe focal point 210, including taking advantage of the fact thatdifferent wavelengths of energy may refract differently through the samematerial, or employing multi-focal lenses such as, by way of example andnot limitation, those described in U.S. Pat. No. 6,010,647.

For illustrative purposes, FIG. 5 depicts another exemplary embodimentof a sorting flow cytometer 220. The sorting flow cytometer 220 includesthe flow path 110 as generally described with respect to FIGS. 3 and 4.Similarly to the sorting flow cytometer 200 depicted in FIG. 4, thesorting flow cytometer 220 omits the first analysis (as well asequipment associated with the first analysis). The sample flow 123 and,in particular, the cells 150, flow toward the objective lens 142. As inpreviously-described embodiments, the objective lens 142 creates a focalpoint 178 at a point 170 in flow path 110. The energy 176 from the cell150 as the cell 150 reaches the point 170 passes through the objectivelens 142, which objective lens 142 is positioned such that the opticalaxis 144 of the objective lens 142 is generally coaxial with the sampleflow 123, and operates to focus the energy 176. The focal point 178 ofthe objective lens 142 is located generally at the point 170, but mayalternatively be located so as to detect the resulting energy 176 fromthe cell 150 slightly after the energy 174 illuminates the cell 150. Oneor more optical elements (such as the beam splitter 202, the filter 186,etc.) may direct the focused energy 182 from the objective lens 142 tothe detector 180.

Referring still to FIG. 5, the depicted sorting flow cytometer 220includes a second analysis illumination source 222. The second analysisillumination source 222 emits energy 224, which may be ultravioletenergy 174. The energy 224 emitted from the second analysis illuminationsource 222 travels through an optical path to the objective lens 142.The objective lens 142 may focus the energy 224 on the focal point 178and, in this manner, the optical paths of the energy 176 and the energy224 may overlap to some degree. Various arrangements of other opticalelements, such as the beam splitter 202 and a filter 226 may operate todirect the energy 224 from the second analysis illumination source 222to the objective lens, and to direct the energy 176 (from the cell 150)from the objective lens 142 to the detector 180.

The controller 166, as described above with respect to FIGS. 3 and 4,operates to interpret signals received (via the connection 184) from thedetector 180 (and the detector 160 if the cytometer 200 includes thefirst analysis) to determine for each cell 150 whether the cell 150 ispart of a desired sub-population of cells. The controller 166 outputs asignal over a connection 230 to a controllable energy source 228. Thecontrollable energy source 228 operates in the same manner as thecontrollable energy source 196 (FIG. 3), outputting energy 232 directedat a point 234.

FIGS. 6A and 6B depict portions 235A and 235B, respectively, of stillother embodiments of a flow cytometer in accordance with thecontemplated methods and apparatus. In each of FIGS. 6A and 6B, cells236 travel in a stream 237 through a flow path 238, which flow path 238changes trajectory at or around a point 239, as described with respectto FIG. 2. Fluidics modeling of and/or precise formation of the flowpath 238 and/or the stream 237 of cells 236 through the flow path 238,and/or the inclusion of additional elements (not shown) to monitor theposition of cells 236, may ameliorate uncertainty otherwise caused bythe change in trajectory at or around the point 239. In this way, theposition and identity of individual cells may remain determinable afterthe trajectory change. FIG. 6A depicts an embodiment in which acontrollable energy source 240, operating in the same manner asdescribed above with respect to FIGS. 3, 4, and 5 (196, 204, and 228,respectively) is positioned such that emitted energy 241 falls incidentupon cells 236 after the cells 236, travel past the point 239 in theflow path 238. FIG. 6A depicts the energy 241 traveling perpendicularlyto the direction in which the cells 236 flow through the flow path 238.Of course, one may appreciate that the controllable energy source 240may alternatively be positioned such that the emitted energy 241 travelsgenerally coaxially with the direction in which the cells 236 flowthrough the flow path 238 (e.g., by again changing the flow direction,and positioning the controllable energy source 240 such that the cells236 in the flow path 238 travel toward the controllable energy source240).

It should be appreciated that a sorting flow cytometer in accordancewith the contemplated methods and apparatus may alternatively employ a“jet-in-air” configuration, as depicted in FIG. 6B. FIG. 6B depicts anozzle 242 emitting a stream 243 of droplets 244. A controllable energysource (not shown) selectively alters droplets by imparting a charge toone or more of the droplets 244. Thereafter, and by way of example andnot limitation, a pair of electrically charged plates 245 may sort thestream 243 of droplets 244 into receptacles 246 according to adetermination by a detector (not shown), as described above.

FIG. 8A depicts the objective lens 142 and a portion of the flow path110 that includes the interrogation region 128. As generally known inthe art, one or more lens elements 250 (e.g., a hemispherical frontlens, a meniscus lens, etc.) act to create a nominal focal point 252. Inthe embodiments described above with respect to FIGS. 3-5, the nominalfocal point 252 is within the sample flow 123 and, in particular, withinthe path of the cells 150 through the flow path 110. The nominal focalpoint 252 defines the apex of a generally conical volume 254 between thenominal focal point 252 and an outer element 256 of the objective lens142 forming a base 253 of the conical volume 254. The conical volume 254may be a right circular conical volume, but may also be an obliqueconical volume. An axis 258 of the cone is generally coaxial with anaxis 260 of the objective lens 142 in embodiments in which the conicalvolume 254 is a right circular conical volume. In such embodiments, theaxes 258 and 260 are further coaxial with an axis of flow 262 within theflow path 110, which axis of flow 262 generally defines the path thatthe cells 150 travel within the flow path 110.

In some embodiments, the focal point 252 of the objective lens 142 issuch that the number of interfaces through which the lateral surface 264of the conical volume 254 passes is minimized. For example, and withreference to FIG. 8A, flow path wall 268A forms the a generallycylindrical transverse flow path 270A, and flow path wall 268B forms agenerally cylindrical flow path 270B that is generally coaxial with theaxis of the conical volume 254. The conical volume 254 in FIG. 8A passesthrough only two interfaces as it enters and exits the materialcomprising the wall 268A. The conical volume 254 passes through aninterface 272 between air 276 and the material comprising the wall 268A,and through an interface 274 between the material comprising the wall268A and fluid 278 in the flow path 110. Moreover, in some embodiments,the wall 268A of the flow path 110 through which the lateral surface 264passes may be generally parallel to the base 253 of the conical volume254. This simplifies the interfaces through which the energy focused bythe objective lens 142 must pass (i.e., the energy does not pass throughany curvilinear surfaces), each of which interfaces may, by operation ofrefraction, affect the focal point 252 of the objective lens 142.Further, the conical volume 254 may be formed of sections 255A, 255B,and 255C of multiple cones 257, 259, and 261 joined together, as shownin FIG. 8B, such as is the case where one or more interfaces (such asthe interfaces 272 and 274) are formed of materials having differingrefractive indices.

Generally, the conical volume 254 must pass through at least the twointerfaces 272 and 274. In some embodiments of the described methods andapparatus, the objective lens 142 may take account of one or more of theinterfaces, for example by accounting for a thickness and refractiveindex of the material forming the interfaces (e.g., the wall 268A).Moreover, in some embodiments, the objective lens 142 may be awater-dipping, water-immersion, or oil-immersion lens, which uses animmersion medium (e.g., water or oil) having a refractive index similarto that of the material forming the interface (e.g., the wall 268A).Thus, as depicted in FIG. 9, some embodiments further reduce distortionof the focal point 252 by minimizing differences between the respectiverefractive indices of the materials through which the conical volume 254passes. In FIG. 9, for example, the conical volume 254 may pass throughwater 280, the wall 268A, and the fluid 278 in the flow path 110. Theobjective lens 142 may be a water-immersion objective lens where, forexample, the wall 268A is made of glass. Alternatively, the objectivelens 142 may be a water-dipping lens in situations in which there is noneed to correct for refraction caused by the wall 268A, such as when thewall 268A is formed of a material with a refractive index similar to orthe same as the fluid 278.

In still further embodiments, and as described fully inconcurrently-filed application Ser. No. ______ (attorney docket no.30752/44821), the walls 268A and 268B of the flow path 110 may be formedof material having a refractive index close to that of the fluid 278(i.e., a material that minimizes the difference between refractiveindices of the materials through which the conical volume 254 passes).For example, materials having a refractive index close to that of waterinclude materials with a refractive index in the range of 1.30 to 1.40,inclusive. Several solid materials in the families of amorphousperfluoropolymers, amorphous fluoropolymers, and perfluoroalkoxypolymers have refractive indices in that range. By way of example andnot limitation, Cytop™, manufactured by Asahi Glass Co., Ltd., andTeflon® AF and Teflon® PFA, manufactured by DuPont™, are three suchmaterials.

In some embodiments, the methods or apparatus may also adjust therefractive index of the fluid 278 such that the refractive index of thefluid 278 is closer to the refractive index of the material forming thewalls 268A and/or 268B of the flow path 110. In particular, the methodsor apparatus may adjust the refractive index of the fluid 278 to bewithin 0.02 of the refractive index of the material forming the walls268A and/or 268B of the flow path 110.

In some cytometers, a portion of the flow path 110, including theinterrogation region 128, is formed in a body 280, such as the body 280shown in FIG. 10. FIG. 10 depicts the body 280 as a rectangular cuboid,having drilled or otherwise formed therein a portion 281 of the flowpath 110. The portion 281 includes a first flow path portion 282generally perpendicular to a surface 284 through which the objectivelens 142 may observe, and a second flow path portion 286 generallyparallel to the surface 284 and intersecting an end 288 of the firstflow path section 282 nearest the surface 284. The body 280, which may,for example, be a cuvette, may be formed of polished quartz, glass,plastic, or other materials as generally known in the art. In someembodiments, the body 280 may be formed, in whole or in part, of amaterial having a refractive index in the range of 1.30 to 1.40,inclusive, such as Cytop™ or Teflon® AF.

In another embodiment, illustrated in FIG. 11, the body 280 includes theportion 281 of the flow path. The portion 281 includes the first flowpath portion 282 generally perpendicular to the surface 284 throughwhich the objective lens 142 may observe. However, in the embodimentdepicted in FIG. 11, the second flow path portion 286 forms a channelhaving an upper edge 290 generally coplanar with the surface 284. Acoverslip 292 disposed on top of the surface 284 may, in someembodiments, allow the use of an objective lens corrected for use withsuch a coverslip 292 to eliminate or minimize the refractive effects ofinterfaces between materials with differing refractive indices.

In still other embodiments, such as that depicted in FIG. 12, the body280 includes a reservoir 294 formed at the intersection of first flowpath portion 282 and the second flow path portion 286. For example, thefirst flow path portion 282 may intersect the reservoir 294 at agenerally planar bottom surface 296 that is generally parallel to thesurface 284. Two parts 286A and 286B of the flow path portion 286 mayconnect to the reservoir 294 at opposing surfaces of the reservoir 294,which may generally have the shape of a flattened cylinder. Thisarrangement may provide further flexibility when adjusting the focalpoint 252 (FIGS. 8 and 9) by, for example, preventing the conical volume254 from passing through the wall 268A of the generally cylindricaltransverse flow path 270A (FIGS. 8 and 9).

FIG. 13 depicts a similar embodiment in which a top edge 298 of thereservoir 294 is coplanar with the surface 284 of the body 280. Awater-dipping objective lens (not shown) may extend into the reservoir294 and, in doing so, may be in contact with fluid flowing through theflow path 110, which may eliminate any interfaces between materials ofdiffering refractive indices.

FIG. 14 depicts yet another embodiment, in which a coverslip 299 isplaced over the exposed reservoir depicted in the embodiment of FIG. 13.

FIG. 15 illustrates a method 300 of selecting a desired sub-populationof cells from a sample of cells. In some embodiments, the method 300, orportions thereof, is stored in a memory as a set of machine-readableinstructions making up a control routine for one or more associatedapparatus. A processor may read the instructions from the memory andexecute the instructions to perform the method 300. In anotherembodiment, the method 300 includes several routines, which routines mayindividually control one or more apparatus, may analyze data collectedby the one or more apparatus, may make one or more determinations basedon the analyzed data, etc. As generally known, a technician or apparatusmay label (e.g., by applying a Hoechst stain) a specimen for analysis(e.g., a collection of sperm cells) (block 305). Labeling the cells maybe accomplished within a sorting flow cytometer, or in a separateprocess or procedure outside of the sorting flow cytometer. Moreover,the particular label applied to the cells may depend upon the cytometricapplication.

In any event, after labeling the cells, a sorting flow cytometer maycreate a flow of sheath fluid in a flow path (block 310). Through aseparate input, the sorting flow cytometer may inject a specimen (i.e.,the labeled cells) into the flow path (block 315), preferably at or nearthe center of the flow of sheath fluid. Also preferably, the specimenenters the flow of sheath fluid slowly relative to the flow of sheathfluid, such that the cells within the specimen (e.g., the sperm cells)align with a long axis parallel to the flow of sheath fluid, and suchthat the cells flow in a generally single-file pattern.

As the cells move through the flow path, an excitation energy source,such as a UV laser, illuminates the specimen (block 320). The excitationenergy source may continually illuminate the flow path, or a routineexecuting on the processor may control the excitation energy source toilluminate the flow path selectively (e.g., only when a specimen ispresent in the flow path).

An objective lens or other focusing means operates to focus energyemitted, transmitted, or reflected from each cell (e.g., fluorescentlight emitted by the label) in a direction coaxial to the flow (block325). That is, the combined sheath flow and specimen within the flowpath move generally toward an objective lens having an optical axis thatis generally coaxial with the flow and, nominally, each cell within thespecimen passes through a focal point of the objective lens. A detectorreceives the focused energy from the objective lens (block 330), andsends a signal representative of the detected energy to a controller. Insome embodiments, the detector may detect individually the focusedenergy from more than 40,000 cells per second, may detect individuallythe focused energy from more than 75,000 cells per second, or may detectindividually the focused energy from more than 100,000 cells per second.

The controller receives the signal representative of the detected energyand analyzes the data (block 335) to determine (at block 340) whetherthe data represent a cell within the desired sub-population, a cell notwithin the desired sub-population, or an indeterminate cell which canneither be determined to be in the desired sub-population nor bedetermined not to be in the desired sub-population. In the latter case,the controller may treat the cell as though the detector determined thatthe cell was not in desired sub-population. If the controller determinesthat the cell is not in the desired sub-population or is indeterminate,the controller may send a signal to a controllable energy source, suchas an infrared laser, to irradiate the cell (e.g., to alter the cell,destroy the cell, render the cell non-viable, etc.) (block 345).Alternatively, if the controller determines that the cell is in thedesired sub-population, the controller may send a signal to thecontrollable energy source (or refrain from sending a signal) such thatthe controllable energy source does not irradiate the cell (block 350).

The apparatus may collect the cells for use and/or further processing(e.g., separating the cells) at the end of the process. In someembodiments, which may include the embodiment depicted in FIG. 15, thecontroller sends a signal to the controllable energy source to leaveunaltered (i.e., not to irradiate) cells determined to be in the desiredsub-population, and the resulting collection of processed cellscomprises a ratio of cells in the desired sub-population of cells tototal unaltered cells greater than or equal to 60%. Further, in someembodiments, which may include the embodiment depicted in FIG. 15, thecontroller sends a signal to the controllable energy source to leaveunaltered (i.e., not to irradiate) cells determined to be in the desiredsub-population, and the resulting collection of processed cellscomprises a ratio of altered cells in the desired sub-population tototal cells in the desired sub-population less than or equal to 50%.

Of course, the method described above reflects one or more embodimentsof the presently described methods, but may also encompass one or moreadditional steps or routines, as described throughout this specificationwith respect to various embodiments. Moreover, some embodiments may omitone or more of the steps or routines described with reference to method300. By way of example and not limitation, in some embodiments, thelabel may auto-fluoresce, thereby eliminating the need to illuminate thespecimen with an illumination energy source. Further, in someembodiments (as described above), the method may reverse blocks 345 and350, allowing cells determined not to be in the desired sub-populationto pass without irradiation by the controllable energy source, whilecausing the controllable energy source to irradiate cells determined tobe in the desired sub-population.

The methods and apparatus provide a number of important advantages overcurrently implemented sorting flow cytometers. As one advantage, thepresently described methods and apparatus do not subject the analytecells, which in some embodiments are mammalian sperm cells, to thejet-in-air configuration commonly used in sorting flow cytometers. Theresult is that a cytometer according to the presently describedembodiments does not expose the analyte cells to the environment outsideof the cytometer or the resulting collision of the sorted droplet with areceptacle, and do not experience the pressures and pressure changesassociated with a nozzle of the jet-in-air configuration. This allowsuse of the cytometer outside of an environment that implements strictconditions of air quality and temperature control (e.g., outside of a“clean room” environment). In fact, the cytometer itself may implementtemperature control to extend the viability of the analyte cells.Moreover, the presently described methods and apparatus may detect andalter the analyte cells faster and/or more accurately, in part becausethe generally coaxial alignment of the objective lens with the flow ofthe analyte through the interrogation area mitigates and/or eliminatesthe problems associated with the anisotropic emission of energy from theanalyte, particularly in embodiments used to sort many types ofmammalian sperm cells. Having read the present description of themethods and apparatus disclosed herein, other advantages of thepresently described methods and apparatus will be apparent to those ofordinary skill in the art.

Although the foregoing text sets forth a detailed description ofnumerous different embodiments, it should be understood that the scopeof protection is defined by the words of the claims to follow. Thedetailed description is to be construed as exemplary only and does notdescribe every possible embodiment because describing every possibleembodiment would be impractical, if not impossible. Numerous alternativeembodiments could be implemented, using either current technology ortechnology developed after the filing date of this patent, which wouldstill fall within the scope of the claims.

Thus, many modifications and variations may be made in the techniquesand structures described and illustrated herein without departing fromthe spirit and scope of the present claims. Accordingly, it should beunderstood that the methods and apparatus described herein areillustrative only and are not limiting upon the scope of the claims. Thespecification above describes at least the following aspects:

1. A method of selecting a first set of cells from a population of cellsincluding the first set of cells and a second set of cells, the methodcomprising:

labeling the population of cells so that the first set of cells can bedistinguished from the second set of cells;

providing a first flow path having a distal end, a proximal end, aninterrogation area disposed between the proximal end and the distal end,and a flow axis;

creating a sheath flow of a sheath fluid through the first flow path,the sheath flow moving toward the proximal end at a first flow rate;

injecting into the sheath flow, at a point upstream from the proximalend, a specimen flow including the population of cells, the specimenflow having initially a second flow rate less than the first flow rate;

providing an excitation energy source, the energy emitted from theexcitation energy source acting on individual cells as they pass throughthe interrogation area and causing emission or transmission of secondaryradiation from the cells;

using an objective lens having an optical axis generally coaxiallyaligned with the flow axis to focus the secondary radiation from theindividual cells as the cells pass through the interrogation area;

detecting the focused secondary radiation from the individual cells;

determining, from the detected secondary radiation, whether theindividual cells are in the first set or the second set; and

selecting cells determined to be in the first set.

2. The method of aspect 1, wherein selecting cells determined to be inthe first set comprises one of derivatizing, killing, damaging,modifying, disrupting, or fragmenting cells not determined to be in thefirst set.

3. The method of aspect 1, wherein selecting cells determined to be inthe first set comprises ejecting the cells in a stream from a nozzle,creating a plurality of droplets from the stream, selectively applying acharge to the droplets, and sorting the droplets according to the chargeof each droplet.

4. The method of any of aspects 1 to 3, wherein labeling the populationof cells comprises staining the cells.

5. The method of any of aspects 1 to 4, wherein causing the emission ofa secondary radiation comprises causing the emission of fluorescentlight.

6. The method of any of aspects 1 to 5, wherein the energy emitted fromthe excitation energy source passes through the objective lens.

7. The method of any of aspects 1 to 6, wherein the cells are spermcells and further wherein the first set of cells comprises either cellswith an X chromosome or cells with a Y chromosome.

8. The method of any of aspects 1 to 7, wherein selecting cellsdetermined to be in the first set comprises using a differentiationenergy source to irradiate cells not determined to be in the first set.

9. The method of aspect 8, wherein the differentiation energy source isa near infrared laser.

10. The method of aspect 8 or aspect 9, wherein the energy emitted fromthe differentiation energy source passes through the objective lens.

11. The method of any of aspects 1 to 10, wherein providing anexcitation energy source comprises providing an ultraviolet laser.

12. The method of aspect 10, further comprising:

selecting a combination of a wavelength of the differentiation energysource, the first flow rate, the second flow rate, and the objectivelens such that a nominal focal point of the objective lens and a nominalfocal point of the differentiation energy source are separated by thedistance that the individual cells will travel through the flow pathbetween detecting the focused secondary radiation and using thedifferentiation energy source to irradiate cells not determined not tobe in the first set.

13. The method of aspect 8 or aspect 10, wherein providing an excitationenergy source comprises providing an attenuated output from thedifferentiation energy source.

14. The method of any of aspects 1 to 13, further comprising providing asecond flow path transverse to the flow axis and disposed at theproximal end of the first flow path, such that after passing through theinterrogation area and reaching the proximal end of the first flow path,the cells move into the second flow path and away from the interrogationarea.

15. The method of any of aspects 1 to 14, wherein providing a flow pathfurther comprises providing a flow path formed of a material having arefractive index in the range of 1.30 to 1.40 inclusive.

16. The method of any of aspects 1 to 15, further comprising adjustingthe refractive index of a solution containing the population of cellssuch that the refractive index of the solution is within 0.02 of therefractive index of the material forming the flow path.

17. An apparatus for detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the apparatuscomprising:

a fluid flow path having:

a first flow section having a flow axis, and

a second flow section,

the first and second flow sections intersecting at a measurement end ofthe first flow section;

an interrogation area disposed at or near the measurement end of thefirst flow section;

a sheath fluid input in fluid flow communication with the fluid flowpath;

a specimen input in fluid flow communication with the fluid flow path;

an objective lens having a nominal focal point and an optical axis, anddisposed at the measurement end of the first flow section, the objectivelens aligned with the first flow section such that the nominal focalpoint is along the flow axis and in the interrogation area, and suchthat the optical axis is generally coaxially aligned with the flow axis;

a detector disposed to detect light focused by the objective lens;

a logic routine communicatively coupled to the detector, operable todetermine whether a cell in the population of specimen cells is one ofthe desired sub-population of cells, and further operable to output asignal based on the determination of whether the cell is one of thedesired sub-population of cells; and

a controllable energy source communicatively coupled to the logicroutine and operable to selectively alter either cells in the desiredsub-population of cells or cells not in the desired sub-population ofcells according to at least the signal output from the logic routine.

18. The apparatus of aspect 17, wherein the controllable energy sourceselectively alters cells by derivatizing, killing, damaging, modifying,disrupting, or fragmenting one or more cells not determined to be in thedesired sub-population.

19. The apparatus of aspect 17 or aspect 18, further comprising anexcitation energy source.

20. The apparatus of aspect 19, wherein energy emitted from theexcitation energy source passes through the objective lens.

21. The apparatus of aspect 19 or aspect 20, wherein the excitationenergy source comprises an attenuator having the controllable energysource as an input.

22. The apparatus of any of aspects 17 to 21, wherein energy emittedfrom the controllable energy source passes through the objective lens.

23. The apparatus of any of aspects 17 to 22, wherein the controllableenergy source comprises a laser.

24. The apparatus of any of aspects 17 to 23, wherein the controllableenergy source comprises a near infrared laser.

25. The apparatus of any of aspects 17 to 24, further comprising a bodyin which the flow path is formed.

26. The apparatus of aspect 25, further comprising a groove forming thesecond flow section in a first surface of the body, wherein themeasurement end of the first flow section intersects the groove at thefirst surface.

27. The apparatus of aspect 25, further comprising:

a first interior channel through the body, extending from a firstsurface of the body to a point in the body and forming the first flowsection; and

a second interior channel through the body, extending from the point inthe body to a second surface of the body.

28. The apparatus of any of aspects 25 to 27, wherein the body is formedof a material having a refractive index between 1.30 and 1.40 inclusive.

29. The apparatus of aspect 28, wherein the material comprises anamorphous perfluoropolymer, an amorphous fluoropolymer, or aperfluoroalkoxy polymer.

30. The apparatus of any of aspects 17 to 29, wherein the objective lensis either a water immersion lens or a water-dipping lens.

31. The apparatus of any of aspects 17 to 30, wherein the population ofspecimen cells comprises sperm cells.

32. The apparatus of aspect 31, wherein the desired population of cellscomprises either cells with an X chromosome or cells with a Ychromosome.

33. A system for detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the systemcomprising:

fluid flow path having a flow axis;

an interrogation area disposed within the fluid flow path;

a sheath fluid input in fluid flow communication with the fluid flowpath;

a first pump in fluid flow communication with the sheath fluid input;

a specimen fluid input in fluid flow communication with the fluid flowpath;

a second pump in fluid flow communication with the specimen fluid input;

an objective lens having a nominal focal point and an optical axis, anddisposed such that the nominal focal point is along the flow axis and inthe interrogation area, and such that the optical axis is generallycoaxially aligned with the flow axis in the interrogation area;

a detector disposed to detect light focused by the objective lens;

a controllable energy source;

a processor communicatively coupled to a computer-readable storagemedium, to the detector, and to the controllable energy source; and

wherein the processor and the controllable energy source cooperate toselectively alter, according to an output from the processor, eithercells in the desired sub-population of cells or cells not in the desiredsub-population of cells.

34. The system of aspect 33, further wherein the processor and thecontrollable energy source cooperate to selectively alter cells in thedesired sub-population of cells by derivatizing, killing, damaging,modifying, disrupting, or fragmenting one or more cells not determinedto be in the desired sub-population of cells.

35. The system of aspect 33 or aspect 34, wherein the energy emittedfrom the controllable energy source passes through the objective lens.

36. The system of any of aspects 33 to 35, wherein the controllableenergy source comprises a near infrared laser.

37. The system of any of aspects 33 to 35, further comprising a bodyformed of a material having a refractive index between 1.30 and 1.40inclusive.

38. The system of any of aspects 33 to 37 wherein the population ofspecimen cells comprises sperm cells.

39. The system of aspect 38, wherein the desired sub-population iseither cells with an X chromosome or cells with a Y chromosome.

40. A method of detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the methodembodied in a set of machine-readable instructions executed on aprocessor and stored on a tangible medium, the method comprising:

controlling the flow of a population of specimen cells through a flowpath having a flow axis;

controlling an illumination source to illuminate an interrogation areathrough which the cells in the population of specimen cells pass;

receiving data from a detector in an optical path having an objectivelens, the objective lens having an optical axis and a nominal focalpoint, the optical axis generally coaxially aligned with the flow axis,the nominal focal point being within the interrogation area;

determining from the received data the presence in the interrogationarea of one of the cells in the population of specimen cells;

determining from the received data whether the one of the specimen cellsis one of the desired sub-population of cells; and

controlling a cell selection energy source, according to at least thedetermination of whether the one of the specimen cells is part of thedesired sub-population of cells.

41. The method of aspect 40, wherein controlling the cell selectionenergy source comprises:

determining the rate of flow through the interrogation area of the oneof the specimen cells; and

selectively irradiating the one of the cells by controlling the cellselection energy source according to the determined rate of flow of theone of the specimen cells through the flow path.

42. The method of aspect 40, wherein controlling the cell selectionenergy source comprises selectively applying a charge to a dropletcontaining a one of the cells.

43. A system for detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the systemcomprising:

a flow path having an interrogation area and a flow axis in theinterrogation area;

control means for controlling a flow of the population of specimen cellsthrough the flow path;

illumination means for illuminating the specimen cells as they passthrough the interrogation area;

an objective lens having an optical axis and a nominal focal point, theoptical axis generally coaxially aligned with the flow axis, the nominalfocal point being within the interrogation area;

detection means for detecting energy focused by the objective lens andproviding data related to the detected energy;

processing means for receiving the data related to the detected energyand for determining whether individual specimen cells passing throughthe interrogation area are one of the desired sub-population;

cell selection means for selectively irradiating the specimen cells; and

cell selection control means for controlling the cell selection meansaccording to at least the determination of whether the individualspecimen cells are one of the desired sub-population.

44. The system of aspect 43, wherein the population of specimen cellscomprises a population of sperm cells and wherein the desiredsub-population of cells comprises sperm cells with an X chromosome.

45. The system of aspect 43, wherein the population of specimen cellscomprises a population of sperm cells and wherein the desiredsub-population of cells comprises sperm cells with an Y chromosome.

46. The system of any of aspects 43 to 45, wherein energy emitted fromthe cell selection means passes through the objective lens beforereaching the specimen cells.

47. The system of any of aspects 43 to 46, wherein at least a part ofthe flow path is formed of a material having a refractive index between1.30 and 1.40 inclusive.

48. A process for detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the processcomprising:

creating a flow carrying a generally single-file procession of specimencells through a flow path;

illuminating the specimen cells as the specimen cells pass through aninterrogation area in the flow path;

positioning an objective lens such that:

an optical axis of the objective lens is generally coaxial with the flowpath,

the flow moves through the flow path toward the objective lens, and

the objective lens has a nominal focal point in the interrogation area;

detecting a parameter of individual specimen cells as the specimen cellspass through the interrogation area;

interpreting the detected parameter of the individual specimen cells todetermine whether the individual specimen cells are one of the desiredsub-population;

selectively derivatizing, killing, damaging, modifying, disrupting, orfragmenting one or more of the population of specimen cells according tothe determination of whether the individual specimen cells are one ofthe desired sub-population of cells; and

collecting the resulting population of processed cells.

49. The process of aspect 48:

wherein the population of specimen cells comprises sperm cells;

wherein the desired sub-population of cells comprises either cellshaving an X chromosome or cells having a Y chromosome; and

wherein detecting a parameter of the individual specimen cells as thespecimen cells pass through the interrogation area comprises detectingthe parameter of more than 40,000 specimen cells per second as the cellspass through the interrogation area.

50. The process of aspect 48, wherein detecting a parameter of theindividual specimen cells as the specimen cells pass through theinterrogation area comprises detecting the parameter of more than 75,000specimen cells per second as the cells pass through the interrogationarea.

51. The process of aspect 48, wherein detecting a parameter of theindividual specimen cells as the specimen cells pass through theinterrogation area comprises detecting the parameter of more than100,000 specimen cells per second as the cells pass through theinterrogation area.

52. The process of any of aspects 48 to 51, wherein cells determined tobe in the desired sub-population are not altered by selectivelyderivatizing, killing, damaging, modifying, disrupting, or fragmentingthe cells, and wherein the resulting population of processed cellscomprises a ratio of cells in the desired sub-population of cells tototal unaltered cells greater than or equal to 60%.

53. The process of any of aspects 48 to 51, wherein cells determined tobe in the desired sub-population are altered by selectivelyderivatizing, killing, damaging, modifying, disrupting, or fragmentingthe cells, and wherein the resulting population of processed cellscomprises a ratio of cells in the desired sub-population of cells tototal altered cells greater than or equal to 60%.

54. The process of any of aspects 48 to 53, wherein the cells determinedto be in the desired sub-population are not altered by selectivelyderivatizing, killing, damaging, modifying, disrupting, or fragmentingthe cells, and wherein the resulting population of processed cellscomprises a ratio of altered cells in the desired sub-population tototal cells in the desired sub-population less than or equal to 50%.

55. The process of any of aspects 48 to 53, wherein the cells determinedto be in the desired sub-population are altered by selectivelyderivatizing, killing, damaging, modifying, disrupting, or fragmentingthe cells, and wherein the resulting population of processes cellscomprises a ratio of unaltered cells in the desired sub-population tototal cells in the desired sub-population less than or equal to 50%.

1. A method of selecting a first set of cells from a population of cellsincluding the first set of cells and a second set of cells, the methodcomprising: labeling the population of cells so that the first set ofcells can be distinguished from the second set of cells; providing afirst flow path having a distal end, a proximal end, an interrogationarea disposed between the proximal end and the distal end, and a flowaxis; creating a sheath flow of a sheath fluid through the first flowpath, the sheath flow moving toward the proximal end at a first flowrate; injecting into the sheath flow, at a point upstream from theproximal end, a specimen flow including the population of cells, thespecimen flow having initially a second flow rate less than the firstflow rate; providing an excitation energy source, the energy emittedfrom the excitation energy source acting on individual cells as theypass through the interrogation area and causing emission or transmissionof secondary radiation from the cells; using an objective lens having anoptical axis generally coaxially aligned with the flow axis to focus thesecondary radiation from the individual cells as the cells pass throughthe interrogation area; detecting the focused secondary radiation fromthe individual cells; determining, from the detected secondaryradiation, whether the individual cells are in the first set or thesecond set; and selecting cells determined to be in the first set. 2.The method of claim 1, wherein selecting cells determined to be in thefirst set comprises one of derivatizing, killing, damaging, modifying,disrupting, or fragmenting cells not determined to be in the first set.3. The method of claim 1, wherein selecting cells determined to be inthe first set comprises: ejecting the cells in a stream from a nozzle;creating a plurality of droplets from the stream; selectively applying acharge to the droplets; and sorting the droplets according to the chargeof each droplet.
 4. The method of claim 1, wherein the energy emittedfrom the excitation energy source passes through the objective lens. 5.The method of claim 1, wherein the cells are sperm cells and furtherwherein the first set of cells comprises either cells with an Xchromosome or cells with a Y chromosome.
 6. The method of claim 1,wherein selecting cells determined to be in the first set comprisesusing a differentiation energy source to irradiate cells not determinedto be in the first set.
 7. The method of claim 6, wherein the energyemitted from the differentiation energy source passes through theobjective lens.
 8. The method of claim 7, further comprising: selectinga combination of a wavelength of the differentiation energy source, thefirst flow rate, the second flow rate, and the objective lens such thata nominal focal point of the objective lens and a nominal focal point ofthe differentiation energy source are separated by the distance that theindividual cells will travel through the flow path between detecting thefocused secondary radiation and using the differentiation energy sourceto irradiate cells not determined not to be in the first set.
 9. Themethod of claim 1, further comprising providing a second flow pathtransverse to the flow axis and disposed at the proximal end of thefirst flow path, such that after passing through the interrogation areaand reaching the proximal end of the first flow path, the cells moveinto the second flow path and away from the interrogation area.
 10. Themethod of claim 1, wherein providing a flow path further comprisesproviding a flow path formed of a material having a refractive index inthe range of 1.30 to 1.40 inclusive.
 11. The method of claim 1, furthercomprising adjusting the refractive index of a solution containing thepopulation of cells such that the refractive index of the solution iswithin 0.02 of the refractive index of a material forming the flow path.12. An apparatus for detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the apparatuscomprising: a fluid flow path having: a first flow section having a flowaxis, and a second flow section, the first and second flow sectionsintersecting at a measurement end of the first flow section; aninterrogation area disposed at or near the measurement end of the firstflow section; a sheath fluid input in fluid flow communication with thefluid flow path; a specimen input in fluid flow communication with thefluid flow path; an objective lens having a nominal focal point and anoptical axis, and disposed at the measurement end of the first flowsection, the objective lens aligned with the first flow section suchthat the nominal focal point is along the flow axis and in theinterrogation area, and such that the optical axis is generallycoaxially aligned with the flow axis; a detector disposed to detectlight focused by the objective lens; a logic routine communicativelycoupled to the detector, operable to determine whether a cell in thepopulation of specimen cells is one of the desired sub-population ofcells, and further operable to output a signal based on thedetermination of whether the cell is one of the desired sub-populationof cells; and a controllable energy source communicatively coupled tothe logic routine and operable to selectively alter either cells in thedesired sub-population of cells or cells not in the desiredsub-population of cells according to at least the signal output from thelogic routine.
 13. The apparatus of claim 12, wherein the controllableenergy source selectively alters cells by derivatizing, killing,damaging, modifying, disrupting, or fragmenting one or more cells notdetermined to be in the desired sub-population.
 14. The apparatus ofclaim 12, further comprising an excitation energy source and whereinenergy emitted from the excitation source passes through the objectivelens.
 15. The apparatus of claim 14, wherein the excitation energysource comprises an attenuator having the controllable energy source asan input.
 16. The apparatus of claim 12, wherein energy emitted from thecontrollable energy source passes through the objective lens.
 17. Theapparatus of claim 12, further comprising a body in which the flow pathis formed.
 18. The apparatus of claim 17, further comprising a grooveforming the second flow section in a first surface of the body, whereinthe measurement end of the first flow section intersects the groove atthe first surface.
 19. The apparatus of claim 17, further comprising: afirst interior channel through the body, extending from a first surfaceof the body to a point in the body and forming the first flow section;and a second interior channel through the body, extending from the pointin the body to a second surface of the body.
 20. The apparatus of claim17, wherein the body is formed of a material having a refractive indexbetween 1.30 and 1.40 inclusive.
 21. The apparatus of claim 20, whereinthe material comprises an amorphous perfluoropolymer, an amorphousfluoropolymer, or a perfluoroalkoxy polymer.
 22. The apparatus of claim12, wherein the objective lens is either a water immersion lens or awater-dipping lens.
 23. The apparatus of claim 12, wherein thepopulation of specimen cells comprises sperm cells and wherein thedesired population of cells comprises either cells with an X chromosomeor cells with a Y chromosome.
 24. A system for detecting and selectivelyaltering a desired sub-population of cells in a population of specimencells, the system comprising: fluid flow path having a flow axis; aninterrogation area disposed within the fluid flow path; a sheath fluidinput in fluid flow communication with the fluid flow path; a first pumpin fluid flow communication with the sheath fluid input; a specimenfluid input in fluid flow communication with the fluid flow path; asecond pump in fluid flow communication with the specimen fluid input;an objective lens having a nominal focal point and an optical axis, anddisposed such that the nominal focal point is along the flow axis and inthe interrogation area, and such that the optical axis is generallycoaxially aligned with the flow axis in the interrogation area; adetector disposed to detect light focused by the objective lens; acontrollable energy source; a processor communicatively coupled to acomputer-readable storage medium, to the detector, and to thecontrollable energy source; and wherein the processor and thecontrollable energy source cooperate to selectively alter, according toan output from the processor, either cells in the desired sub-populationof cells or cells not in the desired sub-population of cells.
 25. Thesystem of claim 24, further wherein the processor and the controllableenergy source cooperate to selectively alter cells in the desiredsub-population of cells by derivatizing, killing, damaging, modifying,disrupting, or fragmenting one or more cells not determined to be in thedesired sub-population of cells.
 26. The system of claim 24, wherein theenergy emitted from the controllable energy source passes through theobjective lens.
 27. The system of claim 24, further comprising a bodyformed of a material having a refractive index between 1.30 and 1.40inclusive.
 28. The system of claim 24, wherein the population ofspecimen cells comprises sperm cells and wherein the desiredsub-population is either cells with an X chromosome or cells with a Ychromosome.
 29. A method of detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the methodembodied in a set of machine-readable instructions executed on aprocessor and stored on a tangible medium, the method comprising:controlling the flow of a population of specimen cells through a flowpath having a flow axis; controlling an illumination source toilluminate an interrogation area through which the cells in thepopulation of specimen cells pass; receiving data from a detector in anoptical path having an objective lens, the objective lens having anoptical axis and a nominal focal point, the optical axis generallycoaxially aligned with the flow axis, the nominal focal point beingwithin the interrogation area; determining from the received data thepresence in the interrogation area of one of the cells in the populationof specimen cells; determining from the received data whether the one ofthe specimen cells is one of the desired sub-population of cells; andcontrolling a cell selection energy source, according to at least thedetermination of whether the one of the specimen cells is part of thedesired sub-population of cells.
 30. The method of claim 29, whereincontrolling the cell selection energy source comprises: determining therate of flow through the interrogation area of the one of the specimencells; and selectively irradiating the one of the cells by controllingthe cell selection energy source according to the determined rate offlow of the one of the specimen cells through the flow path.
 31. Themethod of claim 29, wherein controlling the cell selection energy sourcecomprises selectively applying a charge to a droplet containing a one ofthe cells.
 32. A system for detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the systemcomprising: a flow path having an interrogation area and a flow axis inthe interrogation area; control means for controlling a flow of thepopulation of specimen cells through the flow path; illumination meansfor illuminating the specimen cells as they pass through theinterrogation area; an objective lens having an optical axis and anominal focal point, the optical axis generally coaxially aligned withthe flow axis, the nominal focal point being within the interrogationarea; detection means for detecting energy focused by the objective lensand providing data related to the detected energy; processing means forreceiving the data related to the detected energy and for determiningwhether individual specimen cells passing through the interrogation areaare one of the desired sub-population; cell selection means forselectively irradiating the specimen cells; and cell selection controlmeans for controlling the cell selection means according to at least thedetermination of whether the individual specimen cells are one of thedesired sub-population.
 33. The system of claim 32, wherein thepopulation of specimen cells comprises a population of sperm cells andwherein the desired sub-population of cells comprises: sperm cells withan X chromosome; or sperm cells with a Y chromosome.
 34. The system ofclaim 32, wherein energy emitted from the cell selection means passesthrough the objective lens before reaching the specimen cells.
 35. Thesystem of claim 32, wherein at least a part of the flow path is formedof a material having a refractive index between 1.30 and 1.40 inclusive.36. A process for detecting and selectively altering a desiredsub-population of cells in a population of specimen cells, the processcomprising: creating a flow carrying a generally single-file processionof specimen cells through a flow path; illuminating the specimen cellsas the specimen cells pass through an interrogation area in the flowpath; positioning an objective lens such that: an optical axis of theobjective lens is generally coaxial with the flow path, the flow movesthrough the flow path toward the objective lens, and the objective lenshas a nominal focal point in the interrogation area; detecting aparameter of individual specimen cells as the specimen cells passthrough the interrogation area; interpreting the detected parameter ofthe individual specimen cells to determine whether the individualspecimen cells are one of the desired sub-population; selectivelyderivatizing, killing, damaging, modifying, disrupting, or fragmentingone or more of the population of specimen cells according to thedetermination of whether the individual specimen cells are one of thedesired sub-population of cells; and collecting the resulting populationof processed cells.
 37. The process of claim 36: wherein the populationof specimen cells comprises sperm cells; wherein the desiredsub-population of cells comprises either cells having an X chromosome orcells having a Y chromosome; and wherein detecting a parameter of theindividual specimen cells as the specimen cells pass through theinterrogation area comprises detecting the parameter of more than 40,000specimen cells per second as the cells pass through the interrogationarea.
 38. The process of claim 36, wherein detecting a parameter of theindividual specimen cells as the specimen cells pass through theinterrogation area comprises detecting the parameter of more than 75,000specimen cells per second as the cells pass through the interrogationarea.
 39. The process of claim 36, wherein detecting a parameter of theindividual specimen cells as the specimen cells pass through theinterrogation area comprises detecting the parameter of more than100,000 specimen cells per second as the cells pass through theinterrogation area.
 40. The process of claim 36, wherein cellsdetermined to be in the desired sub-population are not altered byselectively derivatizing, killing, damaging, modifying, disrupting, orfragmenting the cells, and wherein the resulting population of processedcells comprises a ratio of cells in the desired sub-population of cellsto total unaltered cells greater than or equal to 60%.
 41. The processof claim 36, wherein cells determined to be in the desiredsub-population are altered by selectively derivatizing, killing,damaging, modifying, disrupting, or fragmenting the cells, and whereinthe resulting population of processed cells comprises a ratio of cellsin the desired sub-population of cells to total altered cells greaterthan or equal to 60%.
 42. The process of claim 36, wherein the cellsdetermined to be in the desired sub-population are not altered byselectively derivatizing, killing, damaging, modifying, disrupting, orfragmenting the cells, and wherein the resulting population of processedcells comprises a ratio of altered cells in the desired sub-populationto total cells in the desired sub-population less than or equal to 50%.43. The process of claim 36, wherein the cells determined to be in thedesired sub-population are altered by selectively derivatizing, killing,damaging, modifying, disrupting, or fragmenting the cells, and whereinthe resulting population of processes cells comprises a ratio ofunaltered cells in the desired sub-population to total cells in thedesired sub-population less than or equal to 50%.